A force acts on a mass of 16 g for 3 s and then ceases to act. In the next 3 seconds, the mass travels 81 cm. What was the magnitude of the force?

Explanation

While covering the distance of 81 cm, there was no external force on the body and therefore it must have covered this distance with a uniform velocity v, generated when the force was acting on the body.
s = vt or, v = `(s)/(t) = (81)/(3) = 27 " cm " cdot s^(-1)`
If the acceleration on the body due to force was a then
`" "` v = u + at or, 27 = 0 + a`xx`3 or, a = 9 cm `cdot s^(-2)`
`therefore" "` Applied force, F = ma = 16 `xx` 9 = 144 dyn.