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  Solved  Paper-2006

A) \[-0.5J\]              

B)        \[-1.25\,J\]         

C)        1.25 J                    

D)        0.5 J

Correct Answer: B

Solution :

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