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A particle is projected from the top of a tower of height 50m with a velocity of 20m/sec at an angle 30 degrees to the horizontal. Determine

(i) Horizontal distance AB it travel from the foot of the tower.

(ii) The velocity with which it strikes the ground at B.

(iii) Total time taken to reach point B

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1 Answer
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Given:

$U=20m/s \\ . α=30 $

Let O be the origin.

Hence $0 = (0, 0)$

Hence, $B = (X,-50)$ (from the figure)

Hence, $x = ?; y = -50$

Using equation of path,

$Y= x \tan α – 4.9 x^2/ (u \cosα)^2 \\ -50 = X \tan30 – 4.9 \times X^2 /(20cos30)^2\\ X = 75.76 m $

ii)

time = horizontal distance/horizontal speed

$T= X/(u \cos α)= 75.76/(20 \cos30)= 4.37 sec $

iii)

$Vx=Ux = 20 \cos30→ $ (because horizontal speed doesn’t change in a projectile motion)

$$Uy = 20 \sin30$$

$$Vy = ?$$

Using $v= u +at \\ Vy = Uy – g \times T \\ = 20\sin30 – 9.8 \times 4.37 \\ = -32.83 m/s = 32.83 m/s↓ \\ U = 37.12 m/s ↘ θ=62.2$

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