Question

A particle is projected with speed 20m/s at an angle 30° with horizontal. After how much time will the angle between velocity and acceleration be 90°?

Answer 1

Thus it will take 4 seconds to for the angle.

Explanation:

Using newton's second equation of motion along y-direction from point O to P.

- V cos (θ) =  V sin θ  - g x  t

- v cos (30°) = v sin (30°) - g x t

- 20 (√3 ) x (√3 / 2) = 20 x 1/2 - 10 x t

- 30 = 10 - 10 t

10 t = 40

t = 40 / 10  = 4 seconds

Thus it will take 4 seconds to for the angle.