Answer to Question #288111 in Physics for Kev

Question

Jane is walking at such speed so that her kinetic energy is 20 J. What is her speed? It started to rain. Jane runs at a rate of 4.2 m/s. Find the change in her kinetic energy. Jane had a mass of 50 kg.

Answer 1

The kinetic energy is given as follows:

$$K_1 = \dfrac{mv_1^2}{2}$$

Thus, the speed is:

$$v_1 = \sqrt{\dfrac{2K_1}{m}}=\sqrt{\dfrac{2\cdot 20J}{50kg}} \approx 0.89m/s$$

In the second case:

$$K_2 = \dfrac{mv^2_2}{2} = \dfrac{50\cdot 4.2^2}{2} = 441J$$

Thus, the change in kinetic energy is:

$$K_2-K_1 = 441J-20J = 421J$$

Answer. 0.89m/s, 421J.