A 25-g ball is released from rest 80 m above the surface of the Earth.During the fall the total thermal energy of the ball and air increases by15 J.Just before it hits the surface its speed is
A)19 m/s
B)35 m/s
C)40 m/s
D)45 m/s
E)53 m/s

Question

Quizplus · Accepted Answer

Explanation:The total energy of the ball is conserved, so its initial potential energy is equal to its final kinetic energy plus the thermal energy increase:$$mgh = \frac{1}{2}mv^2 + 15 J$$Solving for v, we get:$$v = \sqrt{\frac{2(mgh - 15 J)}{m}}$$Plugging in the given values, we get:$$v = \sqrt{\frac{2(0.025 kg 	imes 9.8 m/s^2 	imes 80 m - 15 J)}{0.025 kg}} = 19 m/s$$

A 25-G Ball Is Released from Rest 80 M Above