Question

A body of mass $2\,kg$ is thrown up vertically with kinetic energy of $490\,J$ . If $g=9.8\,m/s^{2}$ , the height at which the kinetic energy of the body becomes half of the original value, is

• A. 50 m
• B. 25 m
• C. 12.5 m
• D. 19.6 m

Answer 1

Answer: (C)

12.5 m

Answer 2

As body is thrown upwards with kinetic energy of $490 \,J$, so at maximum height it converts wholly to potential energy ie, $U_{\max }=490 \,J$ Let at height $h^{'}$, it becomes just half. $m g h^{'} =\frac{U_{\max }}{2}$ or $h^{'} =\frac{490}{2 \times 2 \times 9.8}=12.5\, m$