ch-4 practice questions 1. A plastic ball in a liquid is acted upon by its weigh

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ch-4 practice questions 1. A plastic ball in a liquid is acted upon by its weight and by a buoyant force. The weight of the ball is The buoyant force has a magnitude of 4.3 N and acts vertically upward. At a given instant, the ball is released from rest. The acceleration of the that instant, including direction, is closest to: A) 19 m/s2, upward B) 0.95 m/s2, upward C) zero D) 0.95 m/$2, downward 36 519 m/s2, downward A block is on a frictionless table, on earth. The block accelerates at 3.0 m/s2 when a 20 N horizontal force is applied to it. The block and table are set up on the moon. The acceleration due to gravity at the surface of the moon is 1.62 m/s. The weight of the block on the moon is closest to: A) 11 N B) 9.5 N C) 8.1 N D) 6.8 N E) 5.5 N 2. 3. If I weigh 741 N on Earth and 5320 N on the surface of a nearby planet, what is the acceleration due to gravity on that planet? A) 70.4 m/s2 B) 51.4 m/s2 C) 61.2 m/s2 D) 81.0 m/s2 4. As shown in Figure 4.3, a woman is straining to lift a large crate, without success. It is too heavy. We denote the forces on the crate as follows: P is the upward force being exerted on the crate by the person, C is the contact force on the crate by the floor, and W is the weight of the crate Figure 4.3

Explanation / Answer

1) The buoyant force which is upward is greater than weight of object so the net force is upward. so the answer is 1.9 m/s^2 upward.

2) F = ma

m = F/ a = 20 /3 = 6.66 kg

Weight of the object on Moon is

W = mg = (6.66)(1.62) = 10.8 N = 11 N

3)

Weight on earth is

W = mg

741 = m (9.8)

m = 741 / 9.8 = 75.61 kg

Weight on nearby planet is

W1 = m g1

g1 = W1 / m= 5320 / 75.61 = 70.4 m/s^2

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