Advertisement Remove all ads

In Figure (I) the Man Walks 2 M Carrying a Mass of 15 Kg on His Hands. in Figure (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 - Physics

In Figure (i) the man walks 2 m carrying a mass of 15 kg on his hands. In Figure (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 ?

Advertisement Remove all ads

Solution 1

 In the second case

Case (i)

Mass, m = 15 kg

Displacement, s = 2 m

Work done `W = Fs cos theta`

Where theta = Angle between force and displacement.

`=mgscostheta = 15 xx 2 xx 9.8 cos 90^theta`

= 0              (∵ `cos 90^@ = 0`)

Case (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 second case.

Solution 2

In Fig. (i), force is applied on the mass, by the man in vertically upward direction but distance is moved along the horizontal.

θ = 90°. W = Fs cos 90° = zero

In Fig. (ii), force is applied along the horizontal and the distance moved is also along the horizontal.

Therefore, θ = 0°.

W = Fs cos θ = mg x s cos 0°

W = 15 x 9.8 x 2 x 1 = 294 joule.

Thus, work done in (ii) case is greater.

  Is there an error in this question or solution?
Advertisement Remove all ads

APPEARS IN

NCERT Class 11 Physics Textbook
Chapter 6 Work, Energy and Power
Q 5.4 | Page 135
Advertisement Remove all ads
Advertisement Remove all ads
Share
Notifications

View all notifications


      Forgot password?
View in app×