Question

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

• A. $-1.25\,J$
• B. $1.25\,J$
• C. $0.5\,J$
• D. $-0.5\,J$

Answer 1

Answer: (A)

$-1.25\,J$

Answer 2

Maximum height reached by the particle

$H_{\max }=\frac{u^{2}}{2 g}=\frac{(5)^{2}}{2 \times 10}=1.25\, m$
Work done $=\vec{ F } \cdot \vec{ d }=F d \cos \theta$
$=m g \times\left(H_{\max }\right) \times \cos 180^{\circ}$
$=0.1 \times 10 \times 1.25 \times(-1)=-1.25\, J$