Figure E-3

-To lift the 5000-N block, the man finds that he must pull 10 m of rope through his hands for every 1 m the block rises. Neglecting the weights of the pulleys and friction, how hard must the man pull on the rope to raise the block?
A)5 N
B)50 N
C)500 N
D)5000 N Which is in accord with
E)Newton's second law.
F)that impulse equals change in momentum.
G)(F × d)input = (F × d)output.
H)mechanical energy can be stored as potential energy.

Question

Figure E-3
 
-To lift the 5000-N block, the man finds that he must pull 10 m of rope through his hands for every 1 m the block rises. Neglecting the weights of the pulleys and friction, how hard must the man pull on the rope to raise the block?
A)5 N 
B)50 N 
C)500 N 
D)5000 N Which is in accord with 
E)Newton's second law. 
F)that impulse equals change in momentum. 
G)(F × d)input = (F × d)output. 
H)mechanical energy can be stored as potential energy.

Quizplus · Accepted Answer

The man must pull with a force of 500 N to lift the 5000-N block, which is in accordance with the principle of work input and output, $(F \times d)_{input} = (F \times d)_{output}$. Since the man pulls 10 m of rope for every 1 m the block rises, the input work is equal to the output work, leading to a reduction in the force required by a factor of 10 (5000 N / 10 = 500 N).

Figure E-3 -To Lift the 5000-N Block, the Man Finds That He