A small block is connected to one end of a massless spring of un - stretched length `4.9 m`. The other end of the spring (see the figure) is fixed. The system lies on a horizontal frictionless surface. The block is stretched by `0.2 m` and released from rest at `t = 0`. It then executes simple harmonic motion with angular frequency `(omega) = (pi//3) rad//s`. Simultaneously at `t = 0`, a small pebble is projected with speed (v) from point (P) at an angle of `45^@` as shown in the figure. Point (P) is at a horizontal distance of `10 m from O`. If the pebble hits the block at `t = 1 s`, the value of (v) is `(take g = 10 m//s^2)`.
.

Options

A. `sqrt(50) m//s`
B. `sqrt(51) m//s`
C. `sqrt(52) m//s`
D. `sqrt(53) m//s`

Answer

A

Explanation

Time of flight for projectile
`T = (2u sin theta)/(g) = 1 sec`
`(2u sin 45)/(g) =1 sec`
`u = (g)/(sqrt(2))`
`u = sqrt(50) m//s`.