First slide

Projection Under uniform Acceleration

Question

A ball is projected upwards from the top of a tower with a velocity of $50 {ms}^{- 1}$ making an angle of 30° with the horizontal. The height of the tower is 70 m. After how many seconds from the instant of throwing will the ball reach the ground ?

Moderate

A

2 s
B

5 s
C

7 s
D

9 s

Solution

The vertically upward component of the velocity of projection $= 50 \sin 30^{\circ} m / s = 25 {ms}^{- 1}$ If t is the time taken to reach the ground, we have $s = - u_{0} t + \frac{1}{2} {gt}^{2}$
or $70 = - 25 t + \frac{1}{2} 10 t^{2}$
or $5 t^{2} - 25 t - 70 = 0 so t = - 2 s or t = - 7 s$
Here, t = -2s is not valid

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App