Question

A particle of mass `100 g` is thrown vertically upwards with a speed of `5 m//s`. The work done by the force of gravity during the time the particle goes up is
A. `-0.5 J`
B. `-1.25 J`
C. `1.25 J`
D. `0.5 J`

Answer 1

Correct Answer - B
The height (h) traversed by particle while going up is :
`h = (u^(2))/(2g) = (25)/(2 xx 9.8)`
Work done by gravity force = mgh

`=0.1 xxg xx (25)/(2xx 9.8) cos 180^(@)`
(Angle between force and displacement is `180^(@)`)
`:. Q =-0.1xx(25)/(2)=-1.25 J`.