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