2024 · Q6
A canon shoots a ball upwards with an initial speed of 100 m/s. The total time of flight of the ball is 20 s before it hits the ground. The ball looses 70% of its speed after hitting the ground. Which among the following is the correct height that the ball will bounce up after its first bounce? (g = 10 m/s²)
general-sciencephysics-mechanics
- A100 m
- B70 m
- C50 m
- D45 m
Explanation
The 20 s flight time is consistent with the launch speed (t = 2u/g = 2×100/10 = 20 s). On impact the ball loses 70% of its speed, retaining 30%, i.e., 0.30 × 100 = 30 m/s upward. The rebound height follows from v² = 2gh, giving h = v²/(2g) = 30²/(2×10) = 900/20 = 45 m. Hence the ball bounces to 45 m after the first bounce.