A particle of mass 100 g is thrown vertically upwards with a speed of `5 ms^(-1)`. The work done by the force of gravity during the time the particle goes up is 

Options

A. `-0.5J`
B. `-1.25J`
C. `1.25 J`
D. `0.5 J`

Answer

B

Explanation

The height (h) traversed by particle while going up is
`h = (u^2)/(2g) = (25)/(2 xx 9.8)" "….(i)`
The force of gravity (= mg) is opposite to the displacment . So the work done by the force of gravity is
`W = - mgh = -0.1 xx 9.8 xx 25/(2 xx 9.8)" (Using (i))"`
` = -0.1 xx 25/2 = -1.25 J`