Question

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. -1.25 J
• C. 1.25 J
• D. 0.5 J

Answer 1

Answer: (B)

-1.25 J

Answer 2

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?] $\therefore\, \quad W=0.1 \times\frac{25}{2}=1.25 J$