6) A bucket is being lowered by a very light rope with a constant downward veloc

Question

6) A bucket is being lowered by a very light rope with a constant downward velocity. The tension in the rope must be A) equal to the weight of the bucket. B) greater than the weight of the bucket C) less than the weight of the bucket. 7) An object is moving with constant non-zero velocity. Which of the following statements about A) A constant force is being applied to it in the direction of motion. B) A constant force is being applied to it in the direction opposite of motion. C A constant force is being applied to it perpendicular to the direction of motion. D) The net force on the object is zero. E) Its acceleration is in the same direction as it velocity. 8) An object of weight W' is in freefall close to the surface of Earth. The magnitude of the force that the object exerts on Earth is A) greater than W B) less than W C) equal to W D) zero. E) cannot be determined without knowing the relative masses of the object and the carth. 9) A fireman is sliding down a fire pole. As he speeds up, he tightens his grip on the pole, thus increasing the vertical frictional force that the pole exerts on the fireman. When the force on his hands equals his weight, what happens to the fireman? A) The fireman comes to a stop. B) The fireman descends with slower and slower speed. C) The fireman descends with a smaller but non-zero acceleration. D) The fireman continues to descend, but with constant speed. E) The acceleration of the fireman is now upward. 10) A person who normally weighs 700 N is riding in an elevator that is moving upward but slowing down at a steady rate. If this person is standing on a bathroom scale inside the elevator what would the scale read? A) more than 700 N B) less than 700 N C) 700 N D) It could be more or less than 700 N, depending on whether the magnitude of the acceleration is greater than or less than 9.8 m/s2.

Explanation / Answer

6. The bucket is moving downward with a constant velocity. That is, there is no net force on the bucket
So the tension in the string is equal to the weight of the bucket
T = m g
Answer A
7. Since the object is moving with a constant velocity, there is no acceleration for the object
So the net force acting on the object must be zero.
Answer D
8. The force between the objects is
F = G M m / (R + h)2
Where G is the gravitational constant, M is the mass of earth, m is the mass of the object, R is the radius of the earth and h is the height
Since the object is close to the surface of earth, we can neglect h compared to R
F = G M m / R2
F = m g
F = W
Where g = G M / R2 is the acceleration due to gravity.
Thus the force due to the falling object is equal to its weight.
the answer is option C.
9. The fireman was sliding with a constant acceleration
m a = W - f
Where f is the frictional force
When the frictional force equals the weight, the net force becomes zero
m a = 0
Thus the acceleration of the fireman becomes zero, but he continues to slide down the pole with a constant velocity
Tha answer is option D

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