Question

A body of mass 10 kg is moving with a uniform velocity of 100 ms -1 . What is the force required to stop the body in 10 seconds

Answer 1

You are given the following informations which are very important to note down in a systematic way :

Mass (m) = 10 kg

Initial velocity (u) = 100 m/s

Final velocity (v) = 0 m/s

Time taken (t) = 10 s

Acceleration (a) = ? m/s²

Now, a = $\frac{v - u}{t}$

Or, $a \: = - \frac{100}{10}$ m/s²

Or, $a = - 10$ m/s²

Here, the negative sign only represents that the acceleration is negative, i.e., retardation occurs.

So, actual retardation = 10 m/s²

Now, F = m × a

Or, F = (10 × 10) N

Or, F = 100 N

[Note : Please ignore the negative sign during calculation, since it represents decrease in velocity (i.e., a identity of retardation). Numerically, we should always accept $\bold{POSITIVE}$ value]