Question

An ace footballer converted a penalty shot by kicking the football with a speed of 108 km h^–1. The estimated force they imparted was 800 N. The mass of the football was 0.4 kg. Calculate the time of contact between their foot and the ball.

Answer 1

Given,

Mass of the football (m) = 0.4 kg

Force imparted (F) = 800 N

Initial velocity (u) = 0

Final velocity (v) = 108 kmh⁻¹

Convert kmh⁻¹ to ms⁻¹ : multiply by `5/18`

108 × `5/18 = 30` ms⁻¹

We know, Force = mass × acceleration = m × `(v - u)/t`

So,

`F = (m(v - u))/t`

or

`t = (m(v - u))/F`

Substituting, we get,

`t = (0.4 xx (30 - 0))/800`

= `12/800`

= 0.015 s

Hence, the time of contact between their foot and the ball is 0.015 s.