Question

An athlete in the Olympic games covers a distance of 100 m in 10 s. his kinetic energy can be estimated to be in the range?
A- 20,000- 50,000 J
B- 2000- 5000 J
C- 200-500 J
D- 200000- 300000 J

Answer 1

We are not given the mass of the athlete. So, we have to take an assumed value. Let us assume the mass of the athlete is 70 Kg. Also, we know that kinetic energy is the energy possessed by the body by virtue of its motion

Step by step answer:
Mass of the athlete, m= 70 kg
To find the velocity of the body we use the formula,
$v=\dfrac{s}{t}=\dfrac{100}{10}=10$m/s
Now to find the kinetic energy,
${{K}_{i}}=\dfrac{m{{v}^{2}}}{2}=\dfrac{70\times {{10}^{2}}}{2}=3500J$

So, the value lies in the range 2000- 5000 J. thus, the correct option is (B).

Additional information:
Energy is a scalar quantity, i.e., it does not depend on direction, and it is always positive. Kinetic energy being negative does not make any sense because we are having a square of velocity and for sure mass can never be negative. Mechanical energy can be summed up as the sum of potential and kinetic energy stored or possessed by the body which is either at rest, either in motion.

Note: Kinetic energy is due to motion and here we had found out the answer by assuming the mass of the athlete. We had calculated the value of velocity from the parameters given in the problem. Energy is measured in the units of Joules.