Question

# A stone is thrown upwards with a speed $$u$$ from the top of a tower. It reaches the ground with a velocity $$3u$$. The height of the tower is

A
u2g
B
2u2g
C
3u2g
D
4u2g

Solution

## The correct option is D $$\cfrac { { 4u }^{ 2 } }{ g }$$Initial velocity$$=+u$$Final velocity $$=-3u$$acc$$=-g$$$$h=$$?$$\quad { v }^{ 2 }={ u }^{ 2 }+2gh\quad$$$$\quad 9{ u }^{ 2 }={ v }^{ 2 }-2gh$$$$8{ u }^{ 2 }=-2gh$$$$h=-\cfrac { 4{ u }^{ 2 } }{ g }$$ (-ve means downward displacement)Physics

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