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)

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 $=m\overrightarrow{\mathbf{g}}\cdot \overrightarrow{\mathbf{h}}$ $=0.1\times g\times \frac{25}{2\times 9.8}\cos {180}^o$ [Angle between force and displacement is ${180}^o$ ] $\therefore$ $W=-0.1\times \frac{25}{2}=-1.25J$