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Speed = 108 km h −1 = 108 × 5 18 = 30 m s -1 . The ball starts from rest, so u = 0, v = 30 m s −1 .
Acceleration a = F m = 800 0.4 = 2000 m s -2 .
Using v = u + at: 30 = 0 + 2000 t , so t = 30 2000 = 0.015 s .
Question 13 — An ace footballer converted a - Questions at the end of the chapter - Chapter 6 - How Forces Affect Motion (Exploration)
Last updated at July 16, 2026 by Teachoo
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.
Time of contact with the football
Convert the speed
108 km h⁻¹ = 108 × 5/18 =
30 m s⁻¹
↓
Find the acceleration
a =
F
m
=
800
0.4
= 2000
m s
-2
↓
Use
v = u + at
with u = 0
30 = 2000 × t
↓
t = 0.015 s
— the boot touches the ball for only 15 milliseconds
