Problem 7.21: The energy required to increase the speed of a certain car from 18 m/s to 28 m/s is 190 kJ .
- Part A: What is the mass of the car? Express your answer to two significant figures and include appropriate units.
- Part B: At what speed is the car’s kinetic energy equal to 190 kJ ? Express your answer to two significant figures and include appropriate units.
Problem 7.27: After hitting a long fly ball that goes over the right fielder's head and lands in the outfield, the batter decides to keep going past second base and try for third base. The 63 kg player begins sliding 3.40 m from the base with a speed of 4.35 m/s.
- Part A: If the player comes to rest at third base, how much work was done on the player by friction?
- Part B: If the player comes to rest at third base, What was the coefficient of kinetic friction between the player and the ground?
Problem 7.1: A pendulum bob swings from point A to point B along the circular arc indicated in the figure (Figure 1).
- Part A: Indicate whether the work done on the bob by gravity is positive, negative, or zero.
- Part B: Indicate whether the work done on the bob by the string is positive, negative, or zero.
Problem 7.10: A 57-kg packing crate is pulled with constant speed across a rough floor with a rope that is at an angle of 36 ∘ above the horizontal.
- Part A: If the tension in the rope is 192 N , how much work is done on the crate by the rope to move it 9.1 m ? Express your answer using two significant figures. W = ? J
Problem 7.40: A new record for running the stairs of the Empire State Building was set on February 3, 2003. The 86 flights, with a total of 1576 steps, was run in 9 minutes and 33 seconds.
- Part A: If the height gain of each step was 0.20 m , and the mass of the runner was 67 kg , what was his average power output during the climb? Give your answer in both watts and horsepower. Express your answer using two significant figures.
- Part B: Express your answer using two significant figures. P = ? hp
Problem 7.42: An ice cube is placed in a microwave oven. Suppose the oven delivers 135 W of power to the ice cube and that it takes 30200 J to melt it.
- Part A: How long does it take for the ice cube to melt? t = ?min
Problem: Two springs, with force constants k1 and k2, are connected in series, as shown in the figure.(Figure 1)
- Part A: How much work is required to stretch this system a distance x from the equilibrium position? Express your answer in terms of the given quantities. W = ?
