1.

A stone is projected horizontally from the top of a tower with a speed of 4m/s lands on the ground at a horizontal distance of 25m from the foot of the tower. Calculate the height of the tower.

Answer»

Firstly we need to find the TIME taken to reach the ground USING horizontal speed and distance covered horizontally

t = x/v

or t = 80/5 = 16 s

Now using the kinematic expression for vertical motion, initial vertical motion being 0 m/s

s = ut + ½ at^2

and taking coordinate axes at the top of tower, noting that gravity acts in a DIRECTION opposite to the positive up direction. If H is height of tower then equation BECOMES

(- h) = 0×16 + ½ (-10) 16^2

or h = 1280 m


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