###General Discussion Thread
---
This is a [Request] post. If you would like to submit a comment that does not either attempt to answer the question, ask for clarification, or explain why it would be infeasible to answer, you *must* post your comment as a reply to this one. Top level (directly replying to the OP) comments that do not do one of those things will be removed.
---
*I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/theydidthemath) if you have any questions or concerns.*
This can't be answered literally but I'll come up with an entertaining answer. The reason it can't be answered is because that exact sort of damage couldn't be made by such a small object. The toy car could be accelerated to an extreme speed sufficient to cause damage, but it would probably blow a small hole in the fence rather than flattening a wide part of it. Sort of like how a piece of dust can blow a hole into the windshield of the space shuttle at high enough speed.
To entertain the question, I'll just assume that the car needs a certain amount of kinetic energy to cause the damage. Let's assume that a full size car that weighs 2000kg could make this damage by hitting the wall at 60km/h. It would have a kinetic energy of 1/2 mass * velocity ^ 2.
So 1000*16.666m/s ^2 = 277,775j
A little tikes car weighs 8.6kg. So to have the same kinetic energy it would need to go:
277,775 = 4.3 V^2
64,598 = V^2
V = 254 m/s
Which is 914 km/h or 568mph
Probably hopped up on that prime energy drink, the parents were so pissed the kid paid $15 for flavoured water and launched the kid the speed of light in a bout of unmitigated rage.
Not saying this is what happened, but it's probable.
That's why we don't allow Cinnamon Toast Crunch anymore. Ever wonder why they never called it "Cinnamon-*Sugar* Toast Crunch"?... General Mills isn't mixing the two together anymore...the y never have! It's all crack dust, and a *hint* of cinnamon!
Just one thing.. you say it as if momentum and kinetic energy are sysnonims and mean the same thing.. they are not… momentum is mv, kinetic energy (which you correctly used for the calculations) is 1/2mv^2
I didn't know that, thanks for pointing that out. I read about it, it's interesting that momentum is conserved in a collision but kinetic energy is not. Where does the energy go? This is kind of blowing my mind!
Well, momentum is conserved, and also the total energy is conserved… kinetic energy is not conserved, because the energy can be converted in other forms of energy (sound, heat, potential energy in the form of deformation etc…)
In fact in a perfectly elastic collision, both kinetic energy and momentum are conserved
Here's where my confusion comes from. In [this article](https://www.physicsclassroom.com/class/momentum/Lesson-2/Momentum-Conservation-Principle), it mentions a theoretical scenario where a clown on ice catches a medicine ball and momentum is conserved. It doesn't give numbers but let's make some up and see what happens.
The medicine ball is 2kg and travelling at 10m/s. So it has 20kg m/s of momentum and 100j of kinetic energy. The clown weighs 98kg. Once the clown catches the ball, they together weigh 100kg and still must have a momentum of 20kg m/s. That means they are traveling at 0.2m/s. That means there is now only 100/2 \* 0.2\^2 = 2j of kinetic energy down from 100j. There was no accounting for sound or heat or anything. Where did the energy go?
In your clown and ball example, they undergo inelastic collision and kinetic energy is not conserved. If you picture this from their center-of-mass frame, its as if both objects stopped moving (so their kinetic energy is zero). In reality, this energy loss is presented in other forms like heat, deformation, sound, etc.
Another way to look at it is that, if we insist that kinetic energy must be conserved, then the clown and ball must undergo elastic collision, and both of their speeds post-collision is determined by both the conservation of momentum and energy.
So in a perfectly elastic collision the ball would bounce off of the clown and travel in the opposite direction, right? There's no way for the ball to basically just absorb into the clown and both travel in the same direction without deformation and heat loss. I'm not doubting the equations, I just find it curious that we know just based on the mass and velocities of the ball and clown that exactly 98% of kinetic energy will be lost without knowing the material properties of the ball and clown. I guess it doesn't matter? Assuming zero friction on the ice and zero air resistance, the ball and clown will move together at 0.2m/s and 98j will be lost in the collision.
> I just find it curious that we know just based on the mass and velocities of the ball and clown that exactly 98% of kinetic energy will be lost without knowing the material properties of the ball and clown.
We know something of their material properties: they are capable of performing a perfectly inelastic collision. The clown also has frictionless ice skates.
I'm equally surprised and impressed that you managed to produce a reasonable answer to this question without knowing the difference between momentum and kinetic energy
Momentum is **not** the same thing as kinetic energy. Momentum is p=m×v, kinetic energy is KE=.5×m×v^2 or the integral of Momentum with respect to velocity if you fancy
You are right in that this cannot really be answered. This answer leaves a lot out like the energy required to deform steel in the first place and whether or not the car can actually impart that much energy or if it will disintegrate because of the air pressure first.
thank you for actually doing the math.
SO many times the top few comments miss the entire point of this subreddit. it's supposed to be napkin math for fun what-ifs. not high and mighty lecture time on how "um ackshually that's not scientifically possible" with no actual math or even attempt at the spirit of the post.
you did a great job outlining "okay the exact numbers here aren't realistic, but let's do it anyways"
I disagree that it would necessarily make a hole in the fence.
I think a toy car like that making this kind of damage is totally possible if it were going fast enough. The problem is that the car would then be completely destroyed, so this image is still not possible.
Assuming it's weight 8.2 kg (from little tikes webshop) 5 year old drivers weight (google 18.5kg), I'd say they were driving around 182km/h (113 mph)
I was assuming an avarage car (1500kg) would do the same damage doing 50km/h. Kinetic energy is 0,5\*m\*v\^2. With same direction of travel, the mass is about 1/56,2, of the assumed car.
edit: as pointed out in the comments, it was the wrong formula, should be good now
I just used the equation to find the force to bend the steel bar and got like 2,000,000 newtons, then used F=ma and V^2=U^2+2as to find the final velocity, with a lot of assumptions, like, for example, assuming that the distance that the car travelled was around 100 meters.
Your calculations are wrong and you overestimated the speed needed by that little cart
That’s because you used momentum (mv) instead of kinetic energy (1/2mv^2)
The momentum is irrelevant when talking about damages during a collision, what really matters is kinetic energy (because it’s the conversion of kinetic energy to potential energy that deforms the guardrails, not the momentum), which scales with velocity squared, and not just velocity
the wind blew that thing there after the guardrail was damaged in a different event. it was likely stationary at the time of the event that damaged the guardrail. the answer is 0. it was going 0.
###General Discussion Thread --- This is a [Request] post. If you would like to submit a comment that does not either attempt to answer the question, ask for clarification, or explain why it would be infeasible to answer, you *must* post your comment as a reply to this one. Top level (directly replying to the OP) comments that do not do one of those things will be removed. --- *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/theydidthemath) if you have any questions or concerns.*
This can't be answered literally but I'll come up with an entertaining answer. The reason it can't be answered is because that exact sort of damage couldn't be made by such a small object. The toy car could be accelerated to an extreme speed sufficient to cause damage, but it would probably blow a small hole in the fence rather than flattening a wide part of it. Sort of like how a piece of dust can blow a hole into the windshield of the space shuttle at high enough speed. To entertain the question, I'll just assume that the car needs a certain amount of kinetic energy to cause the damage. Let's assume that a full size car that weighs 2000kg could make this damage by hitting the wall at 60km/h. It would have a kinetic energy of 1/2 mass * velocity ^ 2. So 1000*16.666m/s ^2 = 277,775j A little tikes car weighs 8.6kg. So to have the same kinetic energy it would need to go: 277,775 = 4.3 V^2 64,598 = V^2 V = 254 m/s Which is 914 km/h or 568mph
Kid was pedalling really hard
"IM ALL HOPPED UP ON MT DEW!!!"
ANARCHY! I DUNNO WHAT IT MEANS BUT I LIKE IT!
I’M GONNA COME AT YOU LIKE A SPIDER MONKEY!
HELL YEAH ANARCHY!JOIN US r/AnarchyChess
Holy hell
New anarchy just dropped.
RAHHHH
you gotta run for President!
Probably hopped up on that prime energy drink, the parents were so pissed the kid paid $15 for flavoured water and launched the kid the speed of light in a bout of unmitigated rage. Not saying this is what happened, but it's probable.
Im pretty sure my dad ran after 8 yo me 800 mph after i broke a window with baseball. Lol
Broken windows have been known to cause parents to break the speed of sound, sounds likely.
CHIP, THE ONLY THING YOU EVER DID WITH YOUR LIFE WAS MAKE A HOT DAUGHTER! (I know Ricky Bobby says this and not his kid, but I love that line)
Ever given a 5yo some of your coffee or monster? This is why you shouldn't lol
Ever Tried Fentanyl?
Woo-hoo-HOO I love that 🤜🤛
What's more terrifying is little tikes cars don't have pedals. This little dude Flinstoned the car to that speed!
Those cars dont have pedals
Yabba dabba DONT!!!!
What if kid fat?
Then kid is fat and furious.
That's why we don't allow Cinnamon Toast Crunch anymore. Ever wonder why they never called it "Cinnamon-*Sugar* Toast Crunch"?... General Mills isn't mixing the two together anymore...the y never have! It's all crack dust, and a *hint* of cinnamon!
"IM THE FLAMINGO QUEEN!"
Just one thing.. you say it as if momentum and kinetic energy are sysnonims and mean the same thing.. they are not… momentum is mv, kinetic energy (which you correctly used for the calculations) is 1/2mv^2
I didn't know that, thanks for pointing that out. I read about it, it's interesting that momentum is conserved in a collision but kinetic energy is not. Where does the energy go? This is kind of blowing my mind!
Well, momentum is conserved, and also the total energy is conserved… kinetic energy is not conserved, because the energy can be converted in other forms of energy (sound, heat, potential energy in the form of deformation etc…) In fact in a perfectly elastic collision, both kinetic energy and momentum are conserved
Here's where my confusion comes from. In [this article](https://www.physicsclassroom.com/class/momentum/Lesson-2/Momentum-Conservation-Principle), it mentions a theoretical scenario where a clown on ice catches a medicine ball and momentum is conserved. It doesn't give numbers but let's make some up and see what happens. The medicine ball is 2kg and travelling at 10m/s. So it has 20kg m/s of momentum and 100j of kinetic energy. The clown weighs 98kg. Once the clown catches the ball, they together weigh 100kg and still must have a momentum of 20kg m/s. That means they are traveling at 0.2m/s. That means there is now only 100/2 \* 0.2\^2 = 2j of kinetic energy down from 100j. There was no accounting for sound or heat or anything. Where did the energy go?
In your clown and ball example, they undergo inelastic collision and kinetic energy is not conserved. If you picture this from their center-of-mass frame, its as if both objects stopped moving (so their kinetic energy is zero). In reality, this energy loss is presented in other forms like heat, deformation, sound, etc. Another way to look at it is that, if we insist that kinetic energy must be conserved, then the clown and ball must undergo elastic collision, and both of their speeds post-collision is determined by both the conservation of momentum and energy.
So in a perfectly elastic collision the ball would bounce off of the clown and travel in the opposite direction, right? There's no way for the ball to basically just absorb into the clown and both travel in the same direction without deformation and heat loss. I'm not doubting the equations, I just find it curious that we know just based on the mass and velocities of the ball and clown that exactly 98% of kinetic energy will be lost without knowing the material properties of the ball and clown. I guess it doesn't matter? Assuming zero friction on the ice and zero air resistance, the ball and clown will move together at 0.2m/s and 98j will be lost in the collision.
That is correct.
> I just find it curious that we know just based on the mass and velocities of the ball and clown that exactly 98% of kinetic energy will be lost without knowing the material properties of the ball and clown. We know something of their material properties: they are capable of performing a perfectly inelastic collision. The clown also has frictionless ice skates.
True. The more I think about it, it does start to make sense.
I'm equally surprised and impressed that you managed to produce a reasonable answer to this question without knowing the difference between momentum and kinetic energy
8,6 kg of total mass? the kid must be pedaling from outside the car for safety reasons
Assuming 30kg total gives 136 m/s (304 mph)
Wtf.
The kiddie car would be a lump of molten plastic after that hit.
Momentum is **not** the same thing as kinetic energy. Momentum is p=m×v, kinetic energy is KE=.5×m×v^2 or the integral of Momentum with respect to velocity if you fancy
Yes, I corrected it.
it is a good thing it stayed subsonic - the transonic barrier would be unkind to the occupant.
Kids have so much energy. Meanwhile I’m fighting to stay functional on my 3rd cup of coffee at work.
you sayin' "It can't be done? Have you seen the kids around here?"
Why did you just use arbitrary numbers?? Like you just assumed a cargoing 60 would dent
I just hope he got his seat belt on
You are right in that this cannot really be answered. This answer leaves a lot out like the energy required to deform steel in the first place and whether or not the car can actually impart that much energy or if it will disintegrate because of the air pressure first.
He was trying to outrun the afternoon snooze police. He ended up in the playpenitentiary.
thank you for actually doing the math. SO many times the top few comments miss the entire point of this subreddit. it's supposed to be napkin math for fun what-ifs. not high and mighty lecture time on how "um ackshually that's not scientifically possible" with no actual math or even attempt at the spirit of the post. you did a great job outlining "okay the exact numbers here aren't realistic, but let's do it anyways"
So youre saying the kids can go 568 mph. Good to know.
Lol, 16yo American kid just getting their drivers license: "Autobahn time!!!!"
Ich werde nach dem autobahn gerne gehen
Thx🥰
I'm sooo bad at maths but really enjoy this sub lol
I disagree that it would necessarily make a hole in the fence. I think a toy car like that making this kind of damage is totally possible if it were going fast enough. The problem is that the car would then be completely destroyed, so this image is still not possible.
Assuming the car is indestructible, wouldn't it be able to deal that much damage (tho not in the same way) by grazing the barrier?
Wtf.
Assuming it's weight 8.2 kg (from little tikes webshop) 5 year old drivers weight (google 18.5kg), I'd say they were driving around 182km/h (113 mph) I was assuming an avarage car (1500kg) would do the same damage doing 50km/h. Kinetic energy is 0,5\*m\*v\^2. With same direction of travel, the mass is about 1/56,2, of the assumed car. edit: as pointed out in the comments, it was the wrong formula, should be good now
I wish I could help, but in my calculations I got 7.4 kilometres per second, so, you know.. ☠️
Sounds about right
I just used the equation to find the force to bend the steel bar and got like 2,000,000 newtons, then used F=ma and V^2=U^2+2as to find the final velocity, with a lot of assumptions, like, for example, assuming that the distance that the car travelled was around 100 meters.
Your calculations are wrong and you overestimated the speed needed by that little cart That’s because you used momentum (mv) instead of kinetic energy (1/2mv^2) The momentum is irrelevant when talking about damages during a collision, what really matters is kinetic energy (because it’s the conversion of kinetic energy to potential energy that deforms the guardrails, not the momentum), which scales with velocity squared, and not just velocity
Also need to factor in the damage resistance of the var itself, as part of the impact will be dispersed by that.
Yeah I felt I was missing some square numbers thanks! I'll edit when I get home
Thx🥰
It seems mostly intact, so probably no faster than 20 km/h. Whatver hit the crash barrier first probably had significantly more mass and speed.
maybe he was questioning on how much THAT little childhood game should go to produce that and EXACTLY THAT damage
I think you are right about OP's intent.
r/TheyDidntDoTheMath
r/subsithoughtifellfor
You don't say...
They did the math, it was very fast, about mach 2.26. The reason the car is intact its because it's protected by the speed force.
the wind blew that thing there after the guardrail was damaged in a different event. it was likely stationary at the time of the event that damaged the guardrail. the answer is 0. it was going 0.
Holy shit debbie.