(b) Given that th- don for u(t) , including num cillates. The resulting - or all quantities is to + d wall. Th from rest at time t = Collisions 2 5. A force exerts an impulse J on an object of mass m, changing its speed from v to u. The force and the object's motion are along the same straight line. Show that the work done by the force is 2 J (u + v) . 6. An electron collides elastically with a hydrogen atom initially at rest. The initial and final motions are along the same straight line. What fraction of the electron's initial kinetic energy is transferred to the hydrogen atom? The mass of the hydrogen atom is 1840 times the mass of the electron. 7. A body of 2.0 kg mass makes an elastic collision with another body at rest and continues to move in the original direction but with one-fourth of its original speed. Calculate the mass of the struck body. 8. A steel ball of mass 0.50 kg is fastened to a cord 70 cm long and is released when the cord is horizontal. At the bottom of its path, the ball strikes a 2.5 kg steel block initially at rest on a frictionless surface. The collision is elastic. Find (a) the speed of the ball and (b) the speed of the block, both just after the collision. 9. A block of mass mi is at rest on a long frictionless table, one end of which is terminated in a wall. Another block of mass my is placed between the first block and the wall and set in motion to the left with constant speed v2. Assuming that all collisions are completely elastic, find the value of my for which both blocks move with the same velocity after my has collided once with m, and once with the wall. Assume the wall to have infinite mass. m1