Work-Energy Theorem Physics Example 3

Follow the full solution, then compare it with the other examples linked below.

medium

0.5 \text{ kg}

ball moving at

8 \text{ m/s}

is hit by a bat that does

25 \text{ J}

of work on it. What is the ball's final speed?

1
Initial KE: $\frac{1}{2}(0.5)(64) = 16 \text{ J}$ . By the work-energy theorem: $W = \Delta KE$ .
2
$25 = \frac{1}{2}(0.5)v_f^2 - 16 \implies \frac{1}{2}(0.5)v_f^2 = 41 \implies v_f = \sqrt{\frac{82}{0.5}} = \sqrt{164} \approx 12.8 \text{ m/s}$

Answer

v_f \approx 12.8 \text{ m/s}

The work-energy theorem accounts for the initial kinetic energy plus the net work done to determine the final kinetic energy and speed of the object.

About Work-Energy Theorem

The net work done on an object by all forces acting on it equals the change in its kinetic energy.

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