In Fig. 6.13(i) the man walks 2 m carrying a mass of 15 kg on his hands. In Fig. 6.13(ii), he walks the same distance pulling the rope behind him. The rope goes over a pulley, and a mass of 15 kg hangs at its other end. In which case is the work done greater? | Learn NCERT solution | Education portal Class 11 Physics | Study online Unit-6 Work, Energy And Power



Q.5(d):- In Fig. 6.13(i) the man walks 2 m carrying a mass of 15 kg on his hands. In Fig. 6.13(ii), he walks the same distance pulling the rope behind him. The rope goes over a pulley, and a mass of 15 kg hangs at its other end. In which case is the work done greater?

 

Answer:-

Work done in fig 6.13 (i)
Mass, m = 15 kg
Displacement, s = 2 m
Work done, W = Fs Cosθ
Where, θ = Angle between force and displacement
= mgs Cosθ = 15 × 2 × 9.8 Cos 900
= 0



Work done in fig 6.13 (ii)
Mass, m = 15 kg
Displacement, s = 2 m
Here, the direction of the force applied on the rope and the direction of the displacement of the rope are same.
Therefore, the angle between them, θ = 0°
Since cos 0° = 1
Work done, W = Fs cosθ = mgs
= 15 × 9.8 × 2 = 294 J

Hence, more work is done in the Fig. 6.13 (ii).