Chapter 10 review


    Quantitative problems
      Section 10.1
      1. Medium A 20 kg chair has 250 J of potential energy relative to the ground. If the chair is dropped from its position, what is its speed when it strikes the ground?
      2. Medium A 60 kg diver drops from a ledge that is 50 ft above the water. What is the speed of the diver upon hitting the water? Give your answer in meters per second and miles per hour.
      3. Medium A large bird with a mass of 1.0 kg is flying at a height of 10.0 m at a speed of 10 m/s. What is the mechanical energy of the bird?
      4. Challenging A 60 kg diver jumps off a diving board upward with an initial velocity of 5 m/s. The diving board is 10 m higher than the water. What is the diver’s speed when just entering the water after the dive?
      Section 10.2
      1. Easy A 6 kg box is traveling at a speed of 10 m/s. Suddenly, it comes across a rough patch in the ground, which exerts a friction force of 40 N on the box. How far will the box go before it stops?
      2. Easy A boy walks up a 10 meter tall snow-covered hill and sleds down. When he reaches the bottom, the boy is moving at 7 m/s. What is the efficiency of the boy's sled ride?
      3. Easy John weighs 80 kg, and eats a 1,000 J candy bar. If his body perfectly transforms the energy in the chocolate into kinetic energy, what is the fastest he can run?
      4. Medium How much distance does it take to stop a car going 30 m/s (67 mph) if the brakes can apply a force equal to one half the car’s weight?
      5. Medium Consider a rubber ball whose bounce has an efficiency of 80%. That means 80% of the kinetic energy before the bounce remains kinetic energy after the bounce. (The rest of the energy is converted to thermal energy.)
        1. If the ball drops from a height of 5 m, how high does it bounce back on the first bounce?
        2. How high does the ball bounce on the second, third, and fourth bounces?
      6. Medium You can only apply a 200 N force but you need to make a 20 kg wagon of mulch travel at a speed of 10 m/s. How far do you have to push the wagon before its speed reaches 10 m/s if it starts from rest? You may assume no friction.
      1. Medium A pitcher for a baseball team can throw a fastball that travels at 45 m/s (100.6 mph). The pitcher throws a ball directly upward with the same energy that he uses to throw a fastball over the plate. Assume that the ball does not experience friction.
        1. How high does the baseball go?
        2. What is the speed of the baseball when the pitcher catches it?
      2. Medium A 10 kg bowling ball sits at the top of a 10 m hill and then slides down its icy hillside.
        1. What is the speed of the bowling ball when it reaches the bottom of the hill?
        2. What is the change in kinetic energy of the system as the bowling ball travels from the top of the hill to the bottom of the hill?
        3. What is the bowling ball’s mechanical energy at the top of the hill?
        4. What is the bowling ball’s mechanical energy at the bottom of the hill?
      3. Medium Juan, who is 60 kg, falls from a height of 20 m on a strange planet that has a large amount of air resistance and a gravity exactly equal to Earth’s. When he reaches the ground, he is traveling 2 m/s.
        1. How efficient was his jump at converting potential into kinetic energy?
        2. How much energy do Juan’s surroundings gain as he jumps?
      4. Challenging Nina, whose mass is 60 kg, is traveling on a bike at 15 m/s at the top of a 3.0 m hill. Nina continues down this hill without pedaling. Assume friction is negligible.
        1. What energy transformation is occurring as she travels down the hill?
        2. How fast is she traveling when she reaches the bottom of the hill?
      5. Challenging A 1,500 kg car begins at rest. A force of 2,000 N is applied to the car for a 20 m stretch in order to accelerate it. At the end of the 20 m, the car is going 5 m/s, and the road gains 21,250 J of thermal energy.
        1. Is energy conserved?
        2. Why does the road gain thermal energy?

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