Problem 10. True or False: Planet X has no air, hence no air resistance. An astronaut standing atop a cliff on Planet X drops a rock down into the lava lake below. If the gravitational potential energy of the rock just before being dropped is PE grav, and its kinetic energy just as it hits the lava is KE, then PE gray > KE. Use the level of the lava lake as the reference line for the potential energy. Problem 11. True or False: A spring cannon is used to launch two balls straightup ward: first, a ball with mass M; then a ball with mass 2M. If the spring in the cannon is compressed by the same amount in both launchings, then it must be the case that the two balls leave the spring cannon with the same kinetic energy. Problem 12. True or False: If you drop an object from rest, then as the object fall sits potential energy is monotonically decreasing. Problem 13. True or False: If you drop an object from rest on a planet with no atmosphere, then as the object falls its kinetic energy is increasing. Problem 14. True or False: If a skateboarder descends down a smooth quarter pipe,with the wheels on his board being fitted with acme unicorn frictionless bearings in them,then his mechanical energy is conserved. Problem 15. True or False: If you drop a large watermelon from the top of a tall building, then, as the watermelon falls, its mechanical energy is not conserved since airdrag is a dissipative force and does negative work on the falling object. Problem 16. True or False: A parachutist is descending at constant speed. This is a situation where the conservation of mechanical energy applies since the net force on the system is zero. Problem 17. True or False: A hot-air balloon ascends at a constant speed upward.This is a situation where the conservation of mechanical energy applies. Problem 18. True or False: A well-oiled pendulum clock swings back and forth. Overone period, it is reasonable to ignore any dissipation and apply the conservation of mechanical energy. Problem 19. True or False: A compressed spring is connected to two gliders initially at rest on a horizontal air track. If the gliders are released from rest and the air track is turned off, so that there is friction between the gliders and the track, then the glider spring system satisfies the conservation of mechanical energy since the track is horizontal so there is no change in gravitational potential. Problem 20. True or False: Consider a typical slider-crank mechanism. Take the system to be the slider-crank and earth. If there is no friction anywhere in the system(no friction in the pins, pivots, or with the slider and guide), and if there is no air dragon the system, then the system's mechanical energy is conserved, and if the system were set in motion, then we'd have a perpetual motion machine.

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Problem 10. True or False: Planet X has no air, hence no air resistance. An astronaut standing atop a cliff on Planet X drops a rock down into the lava lake below. If the gravitational potential energy of the rock just before being dropped is PE grav, and its kinetic energy just as it hits the lava is KE, then PE gray