Physics 115 Test 2A with key

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Unformatted text preview: toward the le ft Answer (b) Apparent weight of ball is to the left, so acceleration is to the right, and thi s must be a centripetal force so the plane is turning to right. Because velocity involves both the direction and the speed, you ca nnot change direction at constant velocity (so this excludes the answers (a) and (c)). Question 14 – The weight in the adjacent weight‐driven clock has a mass of 2 kilogram. It drops 2 cm per hour. What power does the gravitational force exert on the clock? a. 109 10 6 W b. 0.392 W c. 0 W d. 82 103 W Answer (a) Potential energy lost in one hour is mass x g x (change in height) = 2 x 9.8 x (0.02) = 0.392 joules. This the work that is done on the clock. Since power = work/time, we get –4 –6 power = 0.392 / hour x 1 hour / 3,600 sec = 0.392/3,600 = 1.09 x 10 = 10 9 x 10 watts. Question 15 – While you’re weighing yourself on a bathroom scale, you reach out and push downward on a nearby table. This lowers the weight reported by the scale. 2 kg 2 c m per hour Why? a. b. c. d. the scale’s spring constant decreases the scale’s restoring force decreases your apparent weight decreases a stable equilibrium is no longer possible Answer (b) Three forces act on you: weight = m x g (down), spring force from scale (u p), and force from table (up)....
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