Question

From the top of a tower of height 40m a ball is projected upwards with a speed of 20m/s at an angle 30 degree to the horizontal the ball will hit the ground intime

Answer 1

Answer: 4 seconds

Explanation: By using formula of time of flight of a projectile we will find out that;

time of flight = 2usinβ/ g

where u = initial velocity

           β = angle wrt horizontal

           g = acceleration due to gravity.

thus on solving we will get;

(sin30 = 1/2)   therefore time of flight = 2(20)(1/2)/10

time of flight = 2 (but this is time of flight of the projectile which is 40m up in the wrt the ground.

therefore now applying the formula of time of descent in case of vertical motion under the influence of gravity;

time of decent = u/g

where u = initial velocity

          g = acceleration due to gravity

therefore time of descent is equal to;

20/10 = 2 seconds

therefore, total time = time of flight of projectile + time of descent

that is equal to 2 + 2 = 4 seconds