Question

A ball is projected from a building of height 20 metres at a speed of 30 metre per second making an angle 30 with the horizontal. Then time after which the ball strikes the ground is

Answer 1

Answer:

4 seconds

Explanation:

The time the ball takes to reach the ground is only dependant on the vertical component of the velocity.

You can find the vertical component by usinx, where u is the initial velocity(30m/s) and x is the angle of projection(30°),

vertical component= usinx

= 30 x sin30°

=15 m/s

let gravity= 10m/s^2

now to find time use:

S=ut+1/2 at^2

S=displacement

t= time

S=ut+1/2 at^2

-20= 15t+ 1/2×-10t^2

5t^2-15t-20=0

t^2-3t-20=0

t= 4secs

hope it helps

Answer 2

Answer:

4sec

hopes it helps you