Question

1. A sailboat moves north for a distance of 20.0 km when blown by a wind from the exact southwest with a force of 3.50 x 10^4 N. The sailboat travels the distance in 2.5 h. a) How much work was done by the wind? b) What was the wind’s power? Your response should include all of your work and a free-body diagram. Answer:

2. A worker applies 170 N of force on a lever to lift a 1250 N crate 0.10 m. a) If the lever is 100% efficient, how far does he need to push his side? Your response should include all of your work. Answer:

3. A sailor pushes a 160.0 kg crate up a ramp that is 2.50 m high and 15.0 m long onto a loading dock. He exerts a 620.0 N force parallel to the ramp. a) What is the mechanical advantage of the ramp? b) What is the efficiency of the ramp? Your response should include all of your work and a free-body diagram. Answer:

Answer 1

Answer:

1. The work done by the wind was 2.475 x 20^8 J.

The wind’s power was 4.4 x 10^5 W.

F = 3.50 x 10^4 N

S = 20.0 km = 20^4 m

W = 3.50 x 10^4 N x 20^4 m x cos 45 = 3.960 x 10^9 J

2.5 h = 9000 s

3.960 x 10^9/9000 = 4.4 x 10^5

2. If the lever is 100% efficient, the worker needs to push his side 0.735 m.

efficiency = work output/work input x 100

100 = 1250 x 0.1/170d x 100

100/100 = 125/170d

1 = 125/170d

170d = 125

d = 125/170

d = 0.735 m

3. work = force x distance

work = 620 x 15 = 9300 J

work = (160)(9.8)(2.50) = 3920 J

160 x 9.8 = 1568 N

1568/620 = 2.529

mechanical advantage = 2.529

(3920/9300) x 100% = 42.151

efficacy = 42.15%