f.4 phys,,,ball from falling.

Take downward direction to be positive.

a)
u = 0
a = 10 m s-2
s = 8 m

v2 = u2 + 2as
v2 = (0)2 + 2(10)(8)
v2 = 160
v = 12.65

Speed of the ball when it hits the ground = 12.65 m s-1

=====
b)
Let they meet at the height of h m above the ground.
Let they meet at time = t1 s

Consider the falling ball:
u = 0 m s-1
a = 10 m s-1
s = (8 - h) m
t = t1 s

s = ut + (1/2)at2
(8 - h) = (0)t1 + (1/2)(10)t12
8 - h = 5t12
5t12 + h - 8 = 0 ...... (1)

Consider the ball projected upwards from the ground:
u = -12.65 m s-1
s = -h m
a = 10 m s-1
t = t1

s = ut1 + (1/2)at12
(-h) = (-12.65)t1 + (1/2)(10)t12
5t12 - 12.65t1 + h = 0 ..... (2)

(1) - (2):
-8 + 12.65t1 = 0
t1 = 0.6324

Put the value of t1 into (1):
5(0.6324)2 + h - 8 = 0
h = 6

The height from the ground that the balls meet = 6 m

The time that the balls meet = 0.6324 s
=

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