First slide

Work

Question

A boy carrying a box on his head is walking on a level road from one place to another on a straight road is doing no work. The statement is

Easy

A

partly correct
B

correct
C

incorrect
D

insufficient data

Solution

boy carrying a box on horizontal surface is doing no work against gravity, as gravitational force acts vertical down ward, and displacement is horizontal, angle between force of gravitation and displacement are perpendicular to each other hence no work is done by gravitational force.
$w o r k d o n e b y g r a v i t a t i o n a l f o r c e = (F o r c e o f g r a v i t y) . (d i s p l a c e m e n t) f o r c e i s p e r p e n d i c u l a r t o d i s p l a c e m e n t w = F S \cos θ = F S \cos 90 = 0$

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