Question

A boy throws a stone slant wise from a point on the ground with such a speed that it clears the top of a tree and lands on the ground after 4s.if g=10m/s, the height of the tree is

Answer 1

Height of tree = 20  m

Explanation:

Horizontal Range = usin2θ/g

Let say Vertical Velocity = VSinθ

Horizontal Velocity = VCosθ

Time of Flight = 4 sec

Time of Maximum height = 2 sec

Using V = U + at

U = VSinθ

a = - g

t = 2

0 = VSinθ - gt  

=> VSinθ  = (10)(2)

=>  VSinθ  = 20 m/s

Using  V² - U² = 2aS

=> 0² - (20)² = 2(-10)h

=>  h = 20

Height of tree = 20  m

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Answer 2

Answer:

Height of tree = $20 m$

Explanation:

Horizontal Range = usin2θ/g

Let say Vertical Velocity = VSinθ

Horizontal Velocity = VCosθ

Time of Flight = 4 sec  

Time of Maximum height = 2 sec

Using V = U + at  

U = VSinθ

a = - g

t = 2

0 = VSinθ - gt  

=> VSinθ  = (10)(2)

=> VSinθ  = 20 m/s

Using  V² - U² = 2aS

=> 0² - (20)² = 2(-10)h

=>  h = 20

Height of tree = 20m