A ball is thrown vertically upward at 30 m s⁻¹ from the top of a building. It reaches the ground 8 s later. Taking g = 10 m s⁻², enter the height of the building in metres.
Physics · Kinematics Part-1 (one dimension) · Motion under gravity
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Question

A ball is thrown vertically upward at 30 m s⁻¹ from the top of a building. It reaches the ground 8 s later. Taking g = 10 m s⁻², enter the height of the building in metres.

G1 Physics · Accepted Answer

Take upward positive. Ground displacement from the top is −H. Thus −H = 30(8) − 5(64) = 240 − 320 = −80. Hence H = 80 m.