Question

A body of mass 2 kg is thrown up vertically with kinetic energy of 490 J. If $g=9.8\text{ }m/{{s}^{2}},$ 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. So, $mgh=\frac{{{U}_{\max }}}{2}$ or $h=\frac{490}{2\times 2\times 9.8}=12.5\,m$