Question

A discus thrower throws a 5kg discus across the field. How much work does the discus thrower do if the discus is moving 10m/s.

Answer 1

Assuming that the length of the field is 7 meters. So, we have to find the acceleration of the discus to find its applied force

$v^2_f=v^2_0+2ad$

Using the given information, we have

$\begin{gathered} 10^2=0^2+2\cdot a\cdot7 \\ 100=14a \\ a=\frac{100}{14} \\ a\approx7.1m/s^2 \end{gathered}$

Then, we find the force applied

$\begin{gathered} F=m\cdot a=5\cdot7.1 \\ F\approx35.5N \end{gathered}$

At last, we find the work

$W=F\cdot d=35.5\cdot7\approx248.5J$

Hence, the work is 248.5 Joules.