Thread: Momentum

1) A 1.0x10^3 kg plane is trying to make a forced landing on the deck of a 2.0x10^3 kg barge at rest on the surface of a calm sea. The only frictional force to consider is between the plane's wheels and the deck; this braking force is constant and is equal to one-quarter of the plane's weight. What must the minimum length of the barge be for the plane to stop safely on deck, if the plane touches down just at the rear end of the deck with a velocity of 5.0x10^1 m/s toward the front of the barge?

2) A 0.25kg tennis ball is placed right on top of a 1kg volleyball and dropped. Both balls hit the ground at a speed of 3 m/s simultaneously. Find the (upward) velocity of the tennis ball right after it bounces up from the volleyball. Assume elastic collisions. (HINT: the tennis ball will move faster than 3m/s)

I don't have any idea on how to solve this problems. Can someone give me some hints? I would really appreaciate! :-D

1 = 1000 kg plane 2000 kg barge at rest... 250 kg friction..

for every meter the plane lands, the plane will slow down 250 kg per second
5 meters a second.. 5*1000/250= 20 meters... also we'll assume the barge will move with it.. so it'll be 2000/250= 8 .. so the barge will be 12,5% larger than expected. 20* 0,875 = 17,50 meters at least..

2 = kinetic energy = 3 m/s and the mass is 0,25.. by assuming it's elastic the same force will go up again (not true but there are no other values) but this one isn't that hard though