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A particle is projected from the ground ...

A particle is projected from the ground at an angle `30^@` with the horizontal with an initial speed `20 m s^-1`. After how much time will the velocity vector of projectile be perpendicular to the initial velocity ? [in second].

A

4s

B

2s

C

3s

D

Not possible in this case.

Text Solution

Verified by Experts

The correct Answer is:
D
d. `vecu = 20 cos 30 hati + 20 sin 30hatj`
Now, `vecv = 20cos30hati`
`+(20sin30-"gt")hatj`

Let `vecv` be perpendicular to `vecu` at time t, then
`vec v * vecu = 0 rArr t = 4s`
Here time of flight, `T = 2s.` So it is not possible at any instant.
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