question_answer

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                      [AIEEE 2006]

A) \[-0.5J\]

B) \[-125J\]

C) 1.25J

D) 0.5J

Correct Answer: B

Solution :

[b] The height (traversed by particle while going up is

\[h=\frac{{{u}^{2}}}{2g}=\frac{25}{2\times 9.8}\]

Work done by gravity force\[m\,\vec{g}.\vec{h}\]

\[=0.1\times g\times \frac{25}{2\times 9.8}\cos {{180}^{o}}\]

(angle between force and displacement is\[180{}^\circ \])

\[\therefore \]\[W=-0.1\times \frac{25}{2}=-1.25J\]