Question

A particle is projected with velocity 20 m/s, so that it just clears two walls of equal height 10 m, which are at a distance 20 m from each other. The time of passing between the walls is ​

Answer 1

Explanation:

Correct option is

A

2s

Let t be the time of passing between the walls

S=vt

20=20cosθt -------------(i)

vertically

v

2

=u

2

+2aS

v

2

=u

2

sin

2

θ−2g×10

v

2

=u

2

sin

2

θ−20g

v=u+at

0=u−gt

t=

g

v

------------------(ii)

equating eq i and ii

cosθ

1

=2

g

v

squaring both sides and substituting v

cos

2

θ

g

2

=4u

2

sin

2

θ−80g

let sin

2

θ be x

g

2

=16g

2

x(1−x)−8g

2

(1−x)

9=16x−16x

2

+8x

16x

2

−24x+9=0

(4x−3)

2

=0

x=

4

3

sin

2

θ=

4

3

θ= 3 π

therefore time of passing between the walls

t= cosθ

1 =2s