# Problem 1 The brakes of a truck cause it to slow down by applying ...

## Transcribed Text

Problem 1 The brakes of a truck cause it to slow down by applying a retarding force of 860 lb to the truck over a distance of 540 ft. What is the work done by this force on the truck? Problem 2 A person pulls a toboggan for a distance of 35 m along the snow with a rope directed 16° above the snow. The tension in the rope is 76 N. (a) How much work is done on the toboggan by the tension force? (b) How much work is done if the same tension is directed parallel to the snow? Problem 3 When a 0.032-kg golf ball takes off after being hit, its speed is 55 m/s. (a) How much work is done on the ball by the club? (b) Assume that the force of the golf club acts parallel to the motion of the ball and that the club is in contact with the ball for a distance of 0.021 m. Ignore the weight of the ball and determine the average force applied to the ball by the club. Problem 4 A 0.062-sl ball is dropped out of a window that is 15.7 ft above the ground. The ball is caught by a person whose hands are 3.9 ft above the ground. (a) How much work is done on the ball by its weight? (b) What is the gravitational potential energy of the ball, relative to the ground, when it is (b) released and (c) caught? (d) What is the change (PEr PEa) in the ball's gravitational potential energy? Problem 5 A 55-kg skier rides a lift to the top of a mountain. The lift cable is 2400 m long, and can be assumed to not be sagging. The lift makes an angle of 16° with the horizontal. What is the change in the skier's gravitational potential energy? Problem 6 The skateboarder in the drawing starts down the left side of the ramp with an initial speed of 29 ft/s. If non-conservative forces, such as kinetic friction and air resistance, are negligible, what would be the height h of the highest point reached by the skateboarder on the right side of the ramp? Problem 7 Starting at the top of a steep, icy track, a rider jumps onto a sled (known as a skeleton) and proceeds belly down and head first to slide down the track. The track has thirteen turns and drops 97 m in elevation from top to bottom. (a) In the absence of non-conservative forces, such as friction and air resistance, what would be the speed of a rider at the bottom of the track? Assume that the speed of the rider at the beginning of the run is relatively small and can be ignored. (b) In reality, the rider reaches the bottom with a speed of 38 m/s. How much work is done on a 95-kg rider and skeleton by non-conservative forces? Problem 8 Bicyclists in the Tour de France do enormous amounts of work during a race. For example, the average power per kilogram generated by a top rider (m 82.0 kg) is 6.40 w per kilogram of his body mass. (a) How much work does the rider do during a 176-km race in which his average speed is 12.3 m/s? (b) Often, the work done is expressed in nutritional Calories rather than in joules Express the work done in part (a) in terms of nutritional Calories, noting that 4186 joule 1 nutritional Calorie. Problem 9 You are trying to lose weight by working out on a rowing machine. Each time you pull the rowing bar (which simulates the "oars") toward you, it moves a distance of 3.2 ft in a time of 1.6 The readout on the display indicates that the average power you are producing is 98 ft- lb/s. What is the magnitude of the force that you exert on the handle?

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