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Work, energy and power exercises · Physics Playground

ExercisesPhysics

Work, energy and power

16 problems with worked solutions, from Physics and College Physics.

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Learn it first: Energy & Its Conservation

Physics9.1 Work, Power, and the Work–Energy Theorem

ExampleApplying the Work–Energy TheoremAn ice skater with a mass of 50 kg is gliding across the ice at a speed of 8 m/s when her friend comes up from behind and gives her a push, causing her speed to increase to 12 m/s. How much work did the friend do on…

Physics9.2 Mechanical Energy and Conservation of Energy

ExampleApplying the Law of Conservation of EnergyA 10 kg rock falls from a 20 m cliff. What is the kinetic and potential energy when the rock has fallen 10 m?

Physics9.3 Simple Machines

ExampleEfficiency of a LeverThe input force of 11 N acting on the effort arm of a lever moves 0.4 m, which lifts a 40 N weight resting on the resistance arm a distance of 0.1 m. What is the efficiency of the machine?

College Physics7.1 Work: The Scientific Definition

Example 7.1Calculating the Work You Do to Push a Lawn Mower Across a Large LawnHow much work is done on the lawn mower by the person in Figure 7.2(a) if he exerts a constant force of 75.0N at an angle 35º below the horizontal and pushes the mower 25.0m on level ground? Convert the amount of…

College Physics7.2 Kinetic Energy and the Work-Energy Theorem

Example 7.2Calculating the Kinetic Energy of a PackageSuppose a 30.0-kg package on the roller belt conveyor system in Figure 7.4 is moving at 0.500 m/s. What is its kinetic energy?
Example 7.3Determining the Work to Accelerate a PackageSuppose that you push on the 30.0-kg package in Figure 7.4 with a constant force of 120 N through a distance of 0.800 m, and that the opposing friction force averages 5.00 N. (a) Calculate the net work done on the…
Example 7.4Determining Speed from Work and EnergyFind the speed of the package in Figure 7.4 at the end of the push, using work and energy concepts.
Example 7.5Work and Energy Can Reveal Distance, TooHow far does the package in Figure 7.4 coast after the push, assuming friction remains constant? Use work and energy considerations.

College Physics7.3 Gravitational Potential Energy

Example 7.6The Force to Stop FallingA 60.0-kg person jumps onto the floor from a height of 3.00 m. If he lands stiffly (with his knee joints compressing by 0.500 cm), calculate the force on the knee joints.
Example 7.7Finding the Speed of a Roller Coaster from its Height(a) What is the final speed of the roller coaster shown in Figure 7.8 if it starts from rest at the top of the 20.0 m hill and work done by frictional forces is negligible? (b) What is its final speed (again assuming…With a figure

College Physics7.4 Conservative Forces and Potential Energy

Example 7.8Using Conservation of Mechanical Energy to Calculate the Speed of a Toy CarA 0.100-kg toy car is propelled by a compressed spring, as shown in Figure 7.12. The car follows a track that rises 0.180 m above the starting point. The spring is compressed 4.00 cm and has a force constant of 250.0…With a figure

College Physics7.5 Nonconservative Forces

Example 7.9Calculating Distance Traveled: How Far a Baseball Player SlidesConsider the situation shown in Figure 7.17, where a baseball player slides to a stop on level ground. Using energy considerations, calculate the distance the 65.0-kg baseball player slides, given that his initial…With a figure
Example 7.10Calculating Distance Traveled: Sliding Up an InclineSuppose that the player from Example 7.9 is running up a hill having a 5.00º incline upward with a surface similar to that in the baseball stadium. The player slides with the same initial speed, and the frictional…With a figure

College Physics7.7 Power

Example 7.11Calculating the Power to Climb StairsWhat is the power output for a 60.0-kg woman who runs up a 3.00 m high flight of stairs in 3.50 s, starting from rest but having a final speed of 2.00 m/s? (See Figure 7.23.) Figure 7.23 When this woman runs upstairs…With a figure
Example 7.12Calculating Energy CostsWhat is the cost of running a 0.200-kW computer 6.00 h per day for 30.0 d if the cost of electricity is $0.120 per kW⋅h?

College Physics7.8 Work, Energy, and Power in Humans

Example 7.13Calculating Weight Loss from ExercisingIf a person who normally requires an average of 12,000 kJ (3000 kcal) of food energy per day consumes 13,000 kJ per day, he will steadily gain weight. How much bicycling per day is required to work off this extra…