The kinetic energy of an object with mass m and speed v is given by the expression:
Isolate v from the equation and substitute m=60kg and K=1.2x10^4J to find the speed of the student, which is the same as the speed of the car:
![\begin{gathered} \Rightarrow v=\sqrt[]{(2K)/(m)} \\ =\sqrt[]{(2(1.2*10^4J))/(60kg)} \\ =\sqrt[]{\frac{24000\operatorname{kg}\cdot(m^2)/(s^2)}{60\operatorname{kg}}} \\ =\sqrt[]{400\cdot(m^2)/(s^2)} \\ =20\cdot(m)/(s) \end{gathered}]()
Use the conversion factor 1m/s=3.6km/h to write the speed in the requested units:
![v=20\cdot(m)/(s)*\frac{3.6\frac{\operatorname{km}}{h}}{1(m)/(s)}=72(km)/(h)]()
Therefore, the speedometer reading of the car in km/h is:
