Homework problems: Chapter 6

• A horizontal force of 40 N is used to pull a box a distance of 2.5 m across a tabletop. How much work is done by the force?
• A 0.4 kg ball has a velocity of 20 m/s,
  a) What’s the kinetic energy of the ball?
  b) How much work would be required to stop the ball?
  c) If the ball ran 40 m distance to stop, what is the frictional force to make it stop?
• a) What’s the potential energy of a 2 kg rock at top of a hill that is 200 m high?
  b) What’s the potential energy of a ball attached to a spring that is stretched 0.2m from its original unstretched position. (Spring constant k=200 N/m)
• A pendulum bob with a mass of 0.4 kg is released from a position in which the bob is 20 cm above the low point in its swing. What’s the speed of the bob as it passes through the low point in its swing?

5.How do the potential energy and kinetic energy of a freely falling object change during falling process? Explain your answer with principle of energy conservation.