2. a 4.0 kg ball moving to the right at 1.2 m/s collides inelastically with a 1.0 kg ball at rest. what will the velocity of the combined balls be after the collision?

3. an object is lowered into a deep hole in the ground. how does the potential energy of the object change?

4. a real spring does not oscillate forever. instead, it eventually comes to a stop. does this violate the law of conservation of energy? explain why or why not.

5. a boy can raise a rock that weighs 100 n by using a lever and applying a force of 20 n. what is the mechanical advantage of the lever?

2. in inelastic collision, the post-collision velocity will be identical; both balls will be moving together as one. 

3. When the object is lowered the potential energy will decrease, it will be transferred to kinetic energy. Once it reaches the bottom of the deep hole, there will be no kinetic energy and as well as a net loss of potential energy.

4. No. Because according to Law of Conservation of Energy we have KEi+Eloss=0 and KE=-Eloss. The energy lost and the force that causes it to comes to a stop is friction. It is dissipated into forms of energy such as heat.

5. Fin = 20 N ; Fout = 100 N
MA = Fout / Fin = 100 N / 20 N = 5/1 = 5 

This is the answer: body 1 + engine 2