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.

Question

Quizplus · Accepted Answer

When the vertical frictional force equals the fireman's weight, the net force acting on the fireman in the vertical direction becomes zero. According to Newton's second law, when the net force is zero, the acceleration is also zero. This means the fireman will continue moving at whatever speed he has at that moment, without speeding up or slowing down, hence moving with constant speed.

A Fireman Is Sliding Down a Fire Pole