A body is projected at an angle of 30∘ with the horizontal and with a speed of 30ms−1. What is the angle with the horizontal after 1.5 seconds ? (g=10ms−2).
A
0∘
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B
30∘
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C
45∘
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D
60∘
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Solution
The correct option is A0∘ Given, u=30m/s . Let α be the angle of projectile with the horizontal after 1.5 seconds. Let v be the velocity of the projectile after 1.5 seconds. vx=ux=ucosθ⇒vx=30cos30∘=15√3m/s
Using first equation of motion for the vertical component of velocity, we get vy=uy−gt⇒vy=30sin30∘−10×1.5=0
Vertical component of velocity becomes 0 when the body is at the highest point of the projectile. ∴α=0∘