A 6.0-kg block slides along a horizontal surface. If µ_k = 0.20 for the block and surface, at what rate is the friction force changing the mechanical energy of the block at an instant when its speed is 4.0 m/s? A) −59 W B) −47 W C) −71 W D) −82 W E) +71 W

Question

Quizplus · Accepted Answer

The friction force is calculated as f_k = µ_k * m * g = 0.20 * 6.0 kg * 9.8 m/s² = 11.76 N. The rate of change of mechanical energy due to friction is the power, which is the product of the friction force and the velocity: P = f_k * v = 11.76 N * 4.0 m/s = 47.04 W. Since friction does negative work, the power is −47 W.

A 60-Kg Block Slides Along a Horizontal Surface