Question

A soccer player attempting to steal the ball from an opponent was extending her knee at 50 deg/s when her foot struck the opponent's shin pads. If the player's knee was stopped (0 deg/s) within 0.2 seconds, what angular acceleration did the knee experience?

Answer 1

Answer:

$\alpha = -4.36 rad/s^2$

Explanation:

Initial angular speed of the player is given as

$\omega = 50 deg/s$

here we know that

$1 deg = \frac{\pi}{180} rad$

now we know that

$\omega = 50\frac{\pi}{180}$

$\omega = 0.87 rad/s$

now its speed comes to zero in 0.2 s

so angular acceleration is given as

$\alpha = \frac{\omega_f - \omega_i}{\Delta t}$

$\alpha = \frac{0 - 0.87 rad/s}{0.2 s}$

$\alpha = -4.36 rad/s^2$