Explain why a rolling pin flattens a piecrust without encountering very much sliding friction as it moves. 2. What is the momentum of a fly if it's traveling 1 m/s and has a mass of 0.0001 kg? 3. It's easier to injure your knees and legs while hiking downhill than while hiking uphill. Use the concept of energy to explain this observation. 4. Falling into a leaf pile is much more comfortable than falling onto the bare ground. In both cases, you come to a complete stop, so why does the leaf pile feel so much better? 5. The parking brake fails on a 1800kg truck, causing it to roll downhill. At the bottom of the hill, it crashes into a parked car at 3 m/s. The truck comes to a stop in just 0.2 s. What force did the parked car exert on the truck to stop it that quickly? 6. You're at the ice-skating rink with a 5kg bowling ball. The two of you (you and the bowling ball) stand motionless in the middle of the rink so that your combined momentum is zero. You then throw the bowling ball and begin to slide backward. If your momentum is then 12 kg m/s backward, what is speed does the bowling ball have?