### Video Transcript

Find the kinetic energy of a body mass four kilogrammes moving at 36 metres per second. Express your answer in ergs.

We begin by recalling the formula for the kinetic energy of a body. It’s equal to a half of the product of its mass and the square of its velocity. That’s a half 𝑚𝑣 squared. Now, it’s important to note that when we measure kinetic energy using kilogrammes and metres per second, the unit of energy we use is the joule. However, when we measure in grams and centimetres per second, we measure kinetic energy in terms of ergs. And so, we should notice that before we calculate the kinetic energy of the body, it’s sensible to convert the mass into grams and the velocity into centimetres per second.

And so, by recalling that one kilogram is equal to 1000 grams, we multiply by four. And we see that the mass of the body is 4000 grams. We also know that there are 100 centimetres in a metre. So one metre per second is equivalent to 100 centimetres per second. And so, we multiply by 36. And we see that the velocity of the body is 3600 centimetres per second. And so, in ergs, the kinetic energy of the body is a half times 4000 times 3600 squared, which is equal to 2.592 times 10 to the 10th power ergs.