Given data
The mass of the student is m = 60 kg
The kinetic energy possessed by the car is KE = 1.2 x 104 J
The expression for the kinetic energy of the car is given as:
[tex]\begin{gathered} KE=\frac{1}{2}mv^2\ldots.\ldots.(1) \\ v=\sqrt[]{\frac{2\times KE}{m}} \end{gathered}[/tex]Here, the velocity of the car is taken as v.
Substitute the value in the above equation.
[tex]\begin{gathered} v=\sqrt[]{\frac{2\times1.2\times10^4\text{ J}}{60\text{ kg}}} \\ v=20\text{ m/s} \\ v=20\text{ }\frac{m}{s}\times\frac{1\text{ km}}{1000\text{ m}}\times\frac{3600\text{ s}}{1\text{ h}} \\ v=72\text{ km/h} \end{gathered}[/tex]Thus, the car speedometer reading is 72 km/h.
