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Question · Revise, Reflect, Refine, Q13, page 113
An ace footballer converted a penalty shot by kicking the football with a speed of 108 km h⁻¹. The 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.
![Question 13 — An ace footballer - How Forces Affect Moti - [Teachoo] - Questions at the end of the chapter](https://cdn.teachoo.com/803b0fa5-326f-4089-90c1-31ced84bb7ce/animation-for-an-ace-footballer-converted-a-penalty-shot-by-kicking-the-football-with-a-speed-of-108-km-h.-the-force.gif)
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Answer
- Given: u = 0 m s⁻¹, v = 108 km h⁻¹, F = 800 N, m = 0.4 kg
- Convert the speed into m s⁻¹. v = 108 × 1000 / 3600 = 30 m s⁻¹
- Acceleration, a = F / m = 800 / 0.4 = 2000 m s⁻²
- Using v = u + at, 30 = 0 + (2000 × t)
- t = 0.015 s
- Answer: The foot stayed in contact with the ball for 0.015 s.
