Momentum practice problems (answers included)

Review the notes on the blog (2 posts ago) and try these questions and problems (similar to what we did in class today, Monday 4/2).

1.  Give an example of 2 different conservation laws.

2.  What is the mathematical definition of momentum?

3.  What is the conservation of momentum, and when do we think about it (under what specific circumstances)?

4.  A 300-g cart moving at 40 cm/s hits another 300-g at rest.  Friction is very low.  What do you expect will happen exactly?  Give numbers if possible.

5.  A 60-kg figure skater skating at 8 m/s collides directly with a 40-kg skater initially at rest.  Friction is very low and the two become intertwined on the ice.  Calculate the speed of the two of them together after the collision.  (Hint:  First find the momentum of the 60-kg skater, and then use conservation of momentum to solve for the final speed of the two together.  This is like the velcro cart collisions.)

6.  (Challenge problem)  A 2-kg ball is traveling at 4 m/s and it hits another ball (initially at rest).  The 2-kg ball continues to move forward at 3 m/s and the second ball moves forward in the same direction as the original ball at 2 m/s.  How massive is the second ball?  (Hint:  Find the original momentum pre-collision, and then set that equal to the total momentums of the two balls after the collision, keeping the second ball's mass as m.)




Answers

1-3  See notes

4.  Second car moves forward at approximately 40 cm/s.  First car stops.

5.  4.8 m/s

6.  second ball mass is 1 kg

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