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Homework Statement
A boy standing on the top of a building 40m high throws a ball directly aiming to his friend standing on the ground 30m away from the base of the building. If the projection velocity is 20m/s. Find how short will the ball fall from his friend.
Homework Equations
The Attempt at a Solution
From the picture I have attached, AB = 40 m
BC = 30 m
Using pythagoras theorem, we have AC = 50 m
Using tan θ = p/b we have tan θ = 40/30 so, θ = tan^{1}(4/3) = 53°
Now, breaking the components,
Horizontally:
20 * cos53° = 16 m/s
Vertically,
20 * sin 53° = 12m/s
My problem begins here :
1) Which formula do I use, s = ut + 1/2 at^{2} or v = u + at to find the time it takes to reach ground vertically.
2) What's the sign of u and g here.
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