Page 375, fig. 2 Page 374, fig. 1 Page 375, fig. 3.

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A hydraulic lift exerts a force of 12,000 N to lift a car 2 m. How much work is done on the car?

W = F X D

= 12,000 N X 2 m

W = F X D

= 12,000 N X 2 m

= 24,000 Nm

W = F X D

= 12,000 N X 2 m

= 24,000 Nm

= 24,000 J

You exert a force of 0.2 N to lift a pencil off the floor. How much work do you do if you lift it 1.5 m?

W = F X D

= 0.2 N X 1.5 m

W = F X D

= 0.2 N X 1.5 m

= 0.3 Nm

W = F X D

= 0.2 N X 1.5 m

= 0.3 Nm

= 0.3 J

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You cut the lawn with a hand mower. You do 250,000 J of work to move the mower. If the work done by the mower in cutting the lawn is 200,000 J, what is the efficiency of the mower?

E = Wo Wi

E = 200,000 J250,000 J

E = 0.8 X 100% = 80%

You do 1,500 J of work using a hammer. The hammer does 825 J of work on a nail. What is the efficiency of the hammer?

E = Wo Wi

E = 825 J1,500 J

E = Wo Wi

E = 825 J1,500 J

E = 0.55 X 100% = 55%

Suppose you left your lawn mower outdoors all winter. It's now rusty. Of your 250,000 J of work, only 100,000 J go to cutting the lawn. What is the efficiency of the machine now?

E = Wo Wi

E = 100,000 J250,000 J

E = Wo Wi

E = 100,000 J250,000 J

E = 0.4 X 100% = 40%

Page 375, fig. 2 Page 374, fig. 1 Page 375, fig. 3.

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