Question

An object moving at 15 m/s has a kinetic energy of 8500 J. What must be the speed of the same object that has kinetic energy of 6300 J.

Answer 1

Explanations & Calculations

• It is about using the formula of kinetic energy repeatedly.
• The mass of the object is unknown so getting it replaced yields the needed answer.

$\qquad\qquad \begin{aligned} \small E_k&=\small \frac{1}{2}mv^2\\ \small 8500&=\small \frac{1}{2}m(15^2)\cdots(1)\\ \\ \small 6300&=\small \frac{1}{2}m(v^2)\cdots(2)\\ \\ \small (2)\div(1),\\ \\ \small \frac{v^2}{15^2}&=\small \frac{6300}{8500}\\ \small v&=\small \sqrt{\frac{63\times15^2}{85}}\,ms^{-1} \end{aligned}$

• Now you can get things simplified.