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

A) \[-0.5\,J\]

B)  \[-1.25\,J\]

C)  \[1.25\,J\]

D) \[0.5\,J\]

Correct Answer: B

Solution :

 The height \[(h)\]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\[{{180}^{o}}\]] \[\therefore \] \[W=-0.1\times \frac{25}{2}=-1.25\,J\]