Chapter 7: Q9 CQ (page 258)
What is conservative force?
The force for which the work done does not depend on the path taken is known as conservative force.
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(a) What is the available energy content, in joules, of a battery that operates a 2.00-W electric clock for 18 months?
(b) How long can a battery that can supply 8.00×104 J run a pocket calculator that consumes energy at the rate of 1.00×10−3 W?
Suppose the ski patrol lowers a rescue sled and victim, having a total mass of 90.0 kg, down a 60.0º slope at constant speed, as shown in Figure 7.37. The coefficient of friction between the sled and the snow is 0.100.
(a) How much work is done by friction as the sled moves 30.0 m along the hill?
(b) How much work is done by the rope on the sled in this distance?
(c) What is the work done by the gravitational force on the sled?
(d) What is the total work done?
Figure 7.37 A rescue sled and victim are lowered down a steep slope.
Calculate the power output needed for a 950-kg car to climb a 2.00° slope at a constant 30.0 m/s while encountering wind resistance and friction totaling 600 N. Explicitly show how you follow the steps in the Problem-Solving Strategies for Energy.
The person in the figure does work on the lawn mower. Under what conditions would the mower gain energy? Under what conditions would it
lose energy?
A hydroelectric power facility (see Figure 7.38) converts the gravitational potential energy of water behind a dam to electric energy.
(a) What is the gravitational potential energy relative to the generators of a lake of volume , given that the lake has an average height of 40.0 m above the generators?
(b) Compare this with the energy stored in a 9-megaton fusion bomb.
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