A red ball is thrown down with an initial speed of 1.5 m/s from a height of 25 m

Question

A red ball is thrown down with an initial speed of 1.5 m/s from a height of 25 meters above the ground. Then, 0.5 seconds after the red ball is thrown, a blue ball is thrown upward with an initial speed of 23.4 m/s, from a height of 0.8 meters above the ground. The force of gravity due to the earth results in the balls each having a constant downward acceleration of 9.81 m/s2.

1)

What is the speed of the red ball right before it hits the ground?

2)

How long does it take the red ball to reach the ground?

3)

What is the maximum height the blue ball reaches?

4)

What is the height of the blue ball 1.8 seconds after the red ball is thrown?

5)

How long after the red ball is thrown are the two balls in the air at the same height?

Explanation / Answer

For red ball

u =1.5 m/s

v^2 = u ^2 + 2gh = (1.5)^2 + 2×9.81× 0.25   

v = 2.67 m/s

2 ) t = ( v - u ) /g = (2.67 - 1.5 )/ 9.81

t = 0.12 s

3 ) for blue ball

At maximum height

V= 0

h = v^2 -u^2 /2g

= 0-( 23.4 )^2 /2* -9.81

h = 27.9

Total Height attained by Blue ball

= 27.9 + 0.8 = 28.7 m

4) time of flight of Blue ball till 1.8 s from beginning = 1.8 -0.5 = 1.3 s

h = ut + gt^2 /2

= 23.4 * 1.3 + 9.81 × (1.3)^2 /2

= 38.7 m/s

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