Mattiple choice: choose the best answer from provided. Add an explanation for yo

Question

Mattiple choice: choose the best answer from provided. Add an explanation for your answer those You are uncertain. This may get you partial credit iryour choice is incorrect. 1) A car moves along a nat, straight road at a How much work is the normal (or constant velocity, supportive) force doing on the car during this motion? It is equal to your weight B) It is equal to your weight times the radius of the Earth It is equal to the current kinetic energy of the platform D) It is equal to zero E) It is equal to the friction force 2) If you put 15oooos of work into a machine to lift a 2.ooo N slab at a construction site, about how high can the slab be lifted? A) 3x10 B) 152,ooo m C) 148,000 m D) 75 m E) 0,013 m 3) We know that when an object is thrown upward into the air, it is slowing down as it moves higher and higher. Why is it slowing down? A) Its kinetic energy is changing into potential energy B) Gravity is doing positive work on the object C) Most of its energy is becoming heat D) Its potential energy is changing into kinetic energy E) It is gaining momentum 4) What physical quantity can a mechanical device change? A) The force applied to an object B) The distance over which a force acts on an object C) The work done on an object D) Either A or B E) A, B, and C 5) which of the following quantities is ALwAYs positive in value? A) Work B) Momentum C) Kinetic Energy D) Impulse E) velocity 6) Equal forces are used to accelerate a motorcycle and a large truck the same distance down a track. If both started from rest, which object will have a larger kinetic energy when it reaches the end of the track? A) The motorcycle B) The truck C) Both will have the same kinetic energy

Explanation / Answer

1) work done = F.s = F*s*cos(©)

Since angle(©) = 90° ( displacement and normal force are perpendicular to each other)

cos(90°) = 0

W = F*s*cos(90°) = 0

Answer) option d) it is equal to zero

Question 2) work done = force* displacement

W = F*s

s = W/F = 150000/2000 = 75 m

Therefore , height = 75 m

Answer ) option d) 75 m

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