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Chapter 8: 10 CQ (page 211)

In Chapter 7, the work–kinetic energy theorem, W=DK, was introduced. This equation states that work done on a system appears as a change in kinetic energy. It is a special-case equation, valid if there are no changes in any other type of energy such as potential or internal. Give two or three examples in which work is done on a system but the change in energy of the system is not a change in kinetic energy.

Short Answer

Expert verified

The change in energy due to work done in heat engines is not a change in kinetic energy of system and the change in energy due to work done for an object moving in uniform circular motion on a circular path is not a change in kinetic energy are two examples in which change in energy due to work done is not a change in kinetic energy.

Step by step solution

01

Determine the first example for work done on a system such that change in energy is not a change in kinetic energy

When work is done on the piston of the heat engines then fuel is compressed in engine due to change in pressure and temperature. The change in pressure and temperature changes either the heat of system or internal energy of system.

This transfer of work to system changes the energy of system but the change in energy of system is not a change in kinetic energy.

Therefore, the change in energy due to work done in heat engines is not a change in kinetic energy of system.

02

Determine the second example for work done on a system such that change in energy is not a change in kinetic energy

The object moving on a circular path with uniform circular motion consists the same kinetic energy for all positions on circular path but the potential energy of the object on circular path changes with position of object.

The change in the potential energy of object is due to the work done on the object. The kinetic energy is constant so change in energy due to work done is not a change in kinetic energy.

Therefore, the change in energy due to work done for an object moving in uniform circular motion on a circular path is not a change in kinetic energy..

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Most popular questions from this chapter

An older-model car accelerates from 0 to speed v in a time interval of Δt. A newer, more powerful sports car accelerates from 0 to 2v in the same time period. Assuming the energy coming from the engine appears only as kinetic energy of the cars; compare the power of the two cars.

As it plows a parking lot, a snowplow pushes an ever-growing pile of snow in front of it.Suppose a car moving through the air is similarly modeled as a cylinder of area A pushing a growing disk of air in front of it. The originally stationary air is set into motion at the constant speed v of the cylinder as shown in Figure P8.54. In a time interval ∆t, a new disk of air of mass ∆mmust be moved a distance v∆tand hence must be given a kinetic energy 12(Δm)v2.Using this model, show that the car’s power loss owing to air resistance is 12ρAv3and that the resistive force acting on the car is 12ρAv2 , where r is the density of air. Compare this result with the empirical expression 12DρAv2for the resistive force.

A sled of mass m is given a kick on a frozen pond. The kick imparts to the sled an initial speed of 2.00m/s. The coefficient of kinetic friction between sled and ice is 0.100. Use energy considerations to find the distance the sled moves before it stops.

Does the kinetic energy of an object depend on the frame of reference in which its motion is measured? Provide an example to prove this point.

A boy in a wheelchair (total mass 47.0g) has speed1.40m/s at the crest of a slope2.60m high and12.4m long. At the bottom of the slope his speed is 6.20m/s. Assume air resistance and rolling resistance can be modeled as a constant friction force of 41.00N. Find the work he did in pushing forward on his wheels during the downhill ride.
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