Question

A ball has a speed of 15 m/s. Only one external force acts on the ball. After this force acts, the speed of the ball is 7 m/s. Has the force done positive, zero, or negative work on the ball?

Answer 1

Answer:

Negative work

Explanation:

The work-energy theorem states that the work of the resultant forces acting on a particle modifies its kinetic energy:

$W=\Delta K\\W=\frac{mv_f^2}{2}-\frac{mv_0^2}{2}\\W=\frac{m}{2}(v_f^2-v_0^2)\\W=\frac{m}{2}((7\frac{m}{s})^2-(15\frac{m}{s})^2)\\W=\frac{m}{2}(-178\frac{m^2}{s^2})$

Since the mass of the ball has to be positive, the work is negative.