Q. A particle of mass $100g$ 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) $- 0.5\ J$
Explanation
(a) Maximum height reached by the particle
$H_{\max} = \frac{u^{2}}{2g} = \frac{(5)^{2}}{2 \times 10} = 1.25\ m$
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Work done $= \overrightarrow{F}.\overrightarrow{d} = F\ d\cos\theta$
$= mg \times (H_{\max}) \times \cos{(180{^\circ})}$
$= 0.1 \times 10 \times 1.25 \times ( - 1) = - 1.25\ J$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.