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A particle is projected from the ground at an angle 30 degrees with the horizontal with an initial speed of 20m/s. The time after which the velocity vector of projectile becomes perpendicular to the initial vector is a) 4s b) 2s c) 5s d) 6s

A particle is projected from the ground at an angle 30 degrees with the horizontal with an initial speed of 20m/s. The time after which the velocity vector of projectile becomes perpendicular to the initial vector is
a) 4s
b) 2s
c) 5s
d) 6s

Grade:11

1 Answers

Vikas TU
14149 Points
7 years ago
Final velocity to be perpendicular with initiall velocity the final velocity would make the angle 60 degree with the vertical.
Hnece apply laws of eqn.
Vsin60 = 20cos30
V = 20 m/s
and 
Vcos60 = -20sin60 + gt
Hence,
t = (10root3)/10  + 10/10 = > 1.73 + 1 = 1.73 seconds.
that would be approx. 2 seconds.

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