Okay, so I have a test tomorrow afternoon, and I’ve gotten through most of my review. I’m stuck on one because I don’t know what equation to use. You don’t have to work through the problem, just put me in the right direction so that I can do the math myself?
1. When Bowling, your physics buddy asks how much impulse is needed to stop a 10-kg bowling ball moving at 6 m/s. What is your answer?
2. A 2-kg ball of putty moving to the right has a head on inelastic collision with a 1-kg putty ball moving to the left. If the combined blob doesn’t move just after the collision, what can you conclude about the relative speeds of the balls before they collided?
(For this one, am I correct in thinking that the 2-kg putty is moving at half the speed of the 1-kg putty? That just seems logical, but I don’t know what equation to use)
1. impulse is equal to change in momentum (delta p). therefore use your initiall momentum as
pi = mvi and use ur final momentum as pf = mvf. you know the ball needs to be stopped therefore your final velocity and as a result momentum are both 0. so ur answer is impulse = pf – pi
= 0 – pi
remember you will get a negative answer here as the ball is slowing down. this is assuming that the ball speeding up would be positive. this is just one way of setting up your frames of reference. you could just as easily let the condition that the ball slows down be a positive value, but then the condition that the ball speeds up is negative.
2. yes correct, the condition that the two objects hit each and come to rest immediately after impact is such that their two momentums are equal since they are oppositely directed. given by:
p1 = m1v1 and p2 = m2v2 where m1v1 = m2v2. using that last eqn, you can conclude that the 1kg object is travelling at double the speed of the 2kg object. or as you said, that the 2kg object is moving at half the speed of the 1kg object
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