Another question.

[scguy]

I wouldnt normaly post so many questions but i have a mechanics test next week and my teacher takes ages to respond. I would just like to know the best way to answer the attached question which is from a past test paper.

 

Thanks.

[insane_alien]

what is the velocity of B? it says its moving towards A but doesn't give an actual velocity which is required for the question. maybe i missed it cos the image refuses to resize to my screen

[fuhrerkeebs]

If you just want a way to approach it, use the principle of conservation of momentum for problem a. For problem b, just find the difference between the momentum of just car A and the total momentum after the collision (which is just the total momentum altogether, because the momentum is conserved), and them for problem c just say that you assumed that the collision was completely elastic so that no energy was lost. For problem d, just use the force equations and some other elementary formula for velocity and position and such (it's actually simple, if you want I'll go through it for you).

[fuhrerkeebs]

what is the velocity of B? it says its moving towards A but doesn't give an actual velocity which is required for the question. maybe i missed it cos the image refuses to resize to my screen

 

Yeah, now that you mention it the velocity of car B isn't mentioned. I didn't notice that they didn't mention it, however, because of the screen.

[swansont]

for problem c just say that you assumed that the collision was completely elastic so that no energy was lost.

 

 

No, you don't want to do that. It clearly states that they couple together, and that means it's completely inelastic. You'll lose full points for that section.

 

I'd say you are analyzing the collision in the rest frame of B and assign it a speed of zero. You should at least get partial credit (full credit really, if the grader is being fair) for solving the rest if you do it correctly.

[scguy]

I really am not sure what the question is asking for, the reason i posted was because the velocity of car b was not specified. How is the question supposed to be completed in this way?

My mechanics 1 exam is tomorrow btw, i hate not knowing how to approach these ambiguous questions, maybe its a mistake.

btw i dont't know how to resize, it looks pretty rediculous lol. Try saving it and then viewing on picture preview.