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## Homework Statement

"Two boys stand on the roof of an office block. One drops a ball from the roof, the other throws a ball up vertically with an initial velocity of 15 ms^-1. The balls strike the ground 1.88s apart. Calculate the heigh of the office block"

## Homework Equations

x = x_0 + v_0 t + (1/2) a t^2

I learnt formulae with different symbols, and so I found it difficult to recognise relevant equations :(

## The Attempt at a Solution

(no idea if ANY of this is correct so far)

I said the ball going up was ball 1, and the ball which is dropped was ball 2.

I drew a diagram, and worked with ball 1. Firstly, i calculated the time it took for ball 1 to reach a velocity of 0 m/s, which was 1.53 seconds. Then, I calculated the distance from the rooftop to this point, labelled P, which was 11.48 metres. I also labelled office block height as h, and then I said that ball 1 would fall from P to the ground a total of h + 11.48 metres. The time ball 1 takes from P to the ground would be the time that ball 2 takes, plus 1.53 plus 1.88.

My wording was most likely incredibly confusing and incoherent, but basically I'm stuck now. I've tried forming equations such as h+11.48 = 1/2 9.8(t + 3.41)^2 but I suspect I'm forming incorrect equations and have terrible methods...can anybody please take me through this question? I know you won't DO the question which is good - i need to learn it myself - but could you please point out errors in my working and perhaps help me form a suitable equation to solve? :)