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) -1.25J

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\[{{180}^{o}}\]]               \[\therefore \]  \[W=-0.1\times \frac{25}{2}=-1.25J\]