A ball is thrown upwards with a speed of 20m/s from the ground. Another ball is dropped from rest from a building 80m high at the same time
(i) Find the difference in their height after they have fallen for 2s?
(ii) If the balls are along the same line of motion, when will they colide?

Explanation

To solve the problem step by step, we will break it down into two parts as per the question.

### Part (i): Find the difference in their height after they have fallen for 2 seconds.

1. **Determine the height of the first ball (A) after 2 seconds:**
- The ball is thrown upwards with an initial velocity \( u = 20 \, \text{m/s} \).
- The acceleration due to gravity \( g = -9.8 \, \text{m/s}^2 \) (negative because it acts downwards).
- We can use the second equation of motion:
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