Question

a 60 kg student traveling in a car with a constant velocity has the kinetic energy 1.2*10^4 J . what is the speedometer reading of the car in km/h?

Answer 1

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:

`\begin{gathered} KE=(1)/(2)mv^2\ldots.\ldots.(1) \\ v=\sqrt[]{(2* KE)/(m)} \end{gathered}`

Here, the velocity of the car is taken as v.

Substitute the value in the above equation.

`\begin{gathered} v=\sqrt[]{\frac{2*1.2*10^4\text{ J}}{60\text{ kg}}} \\ v=20\text{ m/s} \\ v=20\text{ }(m)/(s)*\frac{1\text{ km}}{1000\text{ m}}*\frac{3600\text{ s}}{1\text{ h}} \\ v=72\text{ km/h} \end{gathered}`

Thus, the car speedometer reading is 72 km/h.