JAMB Physics 1986 Question 12

Question 12

Simple Machines

Figure 4 represents a block-and-tackle pulley system on which an effort of W Newtons supports a load of 120.0 N. If the efficiency of the machine is 40%, then the value of W is

A.28.0 N
B.48.0 N
C.50.0 N
D.288.0 N

Show the answer and explanation

Answer: C (50.0 N)

Explanation

The system has six supporting strands, so VR = 6. MA = 0.4 × 6 = 2.4, and W = 120 ÷ 2.4 = 50 N.