Question

A particle of mass $100g$ is thrown vertically upward with a speed of $5m/s$. The work done by the force of gravity during the time the particle goes up is

• A. $-0.5J$
• B. $-12.5J$
• C. $-1.25J$
• D. $0.5J$

Answer 1

The correct option is C $-1.25J$

Given - $m=100g=0.1kg;u=5m/s;v=0$

By using , $v^2=u^2-2gh$

$0^2=5^2-2gh$

or $h=25/2g$ .................eq1

Force of gravity , $F=mg=0.1g$

Therefore , work done by gravity

$W=Fh\cos 180$

or $W=-0.1g\times 25/2g=-1.25J$