Physics Mechanics Questions

[premed21]

---

Members don't see this ad.

Hey, I have some physics questions. First one is regarding mechanics.

Q) Two cars are going towards each other on ice, and there is minimal friction. One car weights 3000 kg, other car weighs 2000 kg. Both cars collied and stick together upon impact.

Which is conserved?
A) Momentum
B) KE
C) KE & Momentum
D) Neither

My reasonings: KE is not conserved because there is minimal friction. So the question is, is momentum conserved when friction is present? I am unsure about this, so if anyone can explain this I would really appreciate it. Thx in advance.

 

[Phantastic]

For collisions on the MCAT, momentum is always conserved. Remember, it uses velocity (p=mv), so it is a vector--unlike energy, which is a scalar and is only conserved in perfectly elastic collisions.

 

[Phantastic]

Also, if you're curious where that lost energy goes in anything but a perfectly elastic collision: it is transferred to internal energy (which cannot be extracted to do useful work, it's lost)

 

[premed21]

For collisions on the MCAT, momentum is always conserved. Remember, it uses velocity (p=mv), so it is a vector--unlike energy, which is a scalar and is only conserved in perfectly elastic collisions.

Thanks, but wouldn't the velocity have gone down due to the friction? So if velocity decreases, then the momentum would decrease as well would it not? That's the reasoning that I used to pick why momentum is not conserved.

 

[MCAT4life]

it says there are minimal friction, which pretty much tells you to ignore friction. but momentum is ALWAYS conserved on all types of collisions, elastic, inelastic, perfectly inelastic (sticks together). Just remember this and don't look too much into it， if its a conservation of momentum question.

 

[ownage]

Only momentum is conserved. Energy is only conserved in elastic collision and this collision is clearly inelastic.