A boy drops a ball from a cliff 122.5 m high. Find :
(a) How long does it take the ball to fall to the ground.
(b) How far does it fall in the 1st 3 seconds ?
(c) How fast is it going at the end of 3 seconds ?
CBSE Class IX Science SA 2 (3 Marks)
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(a) s = ut + 1/2 gt²
122.5 = 0 x t + 1/2 x 9.8 x t²
122.5 = 4.9 t²
t² = 122.5/4.9
t² = 25
t = √25
=5 sec.
(b) s = ut + 1/2gt²
= 0 x 3 + 1/2 x 9.8 x (3)²
= 1/2 x 9.8 x 9
= 4.9 x 9
= 44.1 m
(c) v = u + gt
v = 0 + 4.9 x 3
v = 4.9 x 3
v = 14.7 m/s
122.5 = 0 x t + 1/2 x 9.8 x t²
122.5 = 4.9 t²
t² = 122.5/4.9
t² = 25
t = √25
=5 sec.
(b) s = ut + 1/2gt²
= 0 x 3 + 1/2 x 9.8 x (3)²
= 1/2 x 9.8 x 9
= 4.9 x 9
= 44.1 m
(c) v = u + gt
v = 0 + 4.9 x 3
v = 4.9 x 3
v = 14.7 m/s
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