Question

a ball is dropped from a cliff it's speed after 4 seconds after it is dropped find.​

Answer 1

Answer:

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A ball is dropped from a cliff. Find

(a) its speed 2s after it is dropped,

(b) its speed when it has fallen through 78.4m , and

(c) the time taken in falling through 78.4m

Hard

Solution

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Velocity after two seconds

v=u+gt

v=0+9.8×2

v=19.6m/s

Velocity when a ball has fallen through 78.4m is given by

v

2

−u

2

=2gh

v

2

−0=2×9.8×78.4

v

2

=1536.64

v=39.2m/s

Let time taken in falling through 78.4m be ts.

h=ut+

2

1

gt

2

78.4=0×t+

2

1

×9.8×t

2

t

2

=

4.9

78.4

t

2

=16

t=4s

Thus time taken in falling through 78.4m is 4s.