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 when 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) measured by particle while goes up is \[w=w\left( 1-\frac{h}{R} \right)\]           Work done by gravity force \[h=\frac{R}{2},\,w=500N\]                 \[\therefore \] [Angle between force and displacement is \[w=500\left( 1-\frac{1}{2} \right)\]]                 \[=\frac{500}{2}=250N\]               \[g=g\left( 1-\frac{2h}{R} \right).\]