A ball is thrown vertically downward with a velocity of 20 m s⁻¹ from the top of a tower. It hits the ground with a velocity of 80 m s⁻¹. Taking g=10 m s⁻², the height of the tower is

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(3) 300 m. Given: initial downward speed u=20 m s⁻¹, final speed v=80 m s⁻¹, g=10 m s⁻². Idea: both the throw and gravity act downward, so use v²=u²+2gh with everything positive downward. h=(v²-u²)/(2g). v²-u²=6400-400=6000. h=(6000)/(20)=300 m.

A ball is thrown vertically downward with a velocity of 20 m s⁻¹ from the top of a tower. It hits the ground with a velocity of 80 m s⁻¹. Taking g=10 m s⁻², the height of the tower is

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