A 50.0-kg crate is being pulled along a horizontal smooth surface. The pulling f

Question

A 50.0-kg crate is being pulled along a horizontal smooth surface. The pulling force is 10.0 N and is directed 20.0 degree above the horizontal. What is the magnitude of the acceleration of the crate? a) 0.0728 m/s^3 b) 0.376 m/s^2 c) 0.0684 m/s^2 d) 0.200 m/^2 e) 0.188 m/s^2 Two objects attract each other gravitationally. If the distance between their centers decreases by a factor of 2, how does the gravitational force between them change? a) The gravitational force remains unchanged. b) The gravitational force decreases by a factor of 4. c) The gravitational force increases by a factor of 2. d) The gravitational force increases by a factor of 4. e) The gravitational force decreases by a factor of 2. A ball is thrown straight up. Neglecting air resistance, which statement is not true regarding the energy of the ball? a) The potential energy decrease when the ball is coming down. b) The kinetic energy increases when the ball is coining down. c) The potential energy decreases while the ball is going up. d) The kinetic energy decreases while the ball is going up. e) The sum of the kinetic energy and potential energy is constant

Explanation / Answer

1] The net force in the horizontal direction is:

Fcos20 - 0 = Fnet = ma

=> 10cos20 = 50a

=> a = 0.188 m/s2.

2] Gravitational force between two bodies is inversely propotional to square of the distance between them.

So, if the distance is decreased by a factor of 2, the force will increase by a factor of 4.

3] Potential energy = mgh

where h is the height from the ground.

So, as the ball goes up, its potential energy increases.

Therefore, statement c] is incorrect.

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