Q. 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 :
AIEEEAIEEE 2008
Solution:
The height (h)traversed by particle while going up is
$h=\frac{u^{2}}{2 g}=\frac{25}{2 \times9.8}$
Work done by gravity force =$m \vec{g}. \vec{h}$
$=0.1\times g\times\frac{25}{2\times9.8} cos\, 180^{\circ}$
[Angle between force and displacement is 180°]
$\therefore \, \quad W=0.1 \times\frac{25}{2}=1.25 J$
