The pair of pulleys shown in (Figure 1) is used to lift a 35-kg block 0.25 m. Th

Question

The pair of pulleys shown in (Figure 1) is used to lift a 35-kg block 0.25 m. The constant upward acceleration of the block during the lift is +2.5 m/s2, and the pulleys and rope have negligible inertia and negligible friction.

A. What is the tension in the pulling rope?

B. What is the tension in the rope from which the block hangs?

C. Determine the magnitude of the force exerted by the upper mount on the top pulley.

D. How much work is done by the person pulling the rope in lifting the block 0.25 m?

E. By how much does the kinetic energy of the block change in this process?

F. How much work is done on the block by the rope attached to it?

G. How much work does the ceiling do in this process?

H. How much work does Earth do on the block?

Explanation / Answer

m = 35 kg

d = 0.25 m

a = + 2.5 m/sec2  

Td = 35 X 10 = 350 N

Tb = Tc = 175 N

a )

the tension in the pulling rope is = 175 N

b )

the tension in the rope from which the block hangs

T = 35 X 10

= 350 N

c )

the magnitude of the force exerted by the upper mount on the top pulley is

Ff = Td + Tb + Tc

= 175 + 175 + 175

= 525 N

d )

work is done by the person pulling the rope in lifting the block 0.25 m is

W = F X d

W = 43.75 J

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