# A rock thrown horizontally from the top of a water tower lands 20 m from the base of the tower. If the rock was initially thrown at a velocity of 10.0 m/s, what is the final velocity of the rock at...

A rock thrown horizontally from the top of a water tower lands 20 m from the base of the tower. If the rock was initially thrown at a velocity of 10.0 m/s, what is the final velocity of the rock at the instant it hits the ground?

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### 1 Answer

The rock is thrown horizontally from the top of a water tower and it lands 20 m from the base of the tower. It was initially thrown at a horizontal velocity of 10 m/s.

There is no acceleration acting on the rock in the horizontal direction. The time taken by the rock to travel 20 m at 10 m/s is 20/10 = 2 s.

The acceleration due to gravity of 9.8 m/s^2 acts vertically downwards on the rock. It increases the velocity of the rock in two seconds to 9.8*2 = 19.6 m/s when it hits the ground.

On striking the ground there are two components of the velocity. This gives the magnitude as sqrt(19.6^2 + 10^2) = 22 m/s. The direction of velocity makes an angle of arc tan(19.6/10) = 62.96 degrees with the horizontal.

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