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Question

Sneha throws a pillow up into the air which returns to her hands after 3 s. Then pick out the correct statements from the following.

A
After 2 s, the pillow is at a height of 6.4 m.
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B
The pillow reaches a maximum height of 11 m.
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C
After 2 s, the pillow is at a height of 9.8 m.
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D
The pillow is thrown up with a velocity of 14.7 m s1.
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Solution

The correct options are
B The pillow reaches a maximum height of 11 m.
C After 2 s, the pillow is at a height of 9.8 m.
D The pillow is thrown up with a velocity of 14.7 m s1.
Given:
Total time taken by the pillow to go up and fall back into Sneha's hands, T=3 s
When the pillow is at its highest position in the air, its velocity, v=0
The pillow takes equal time for going up and falling down Time taken for the upward journey, t1=T2=1.5 s

From bottom to top point:
Using the first equation of motion,
v=ugt
0=u9.8×1.5
u=9.8×1.5=14.7 m s1

From bottom to top point:
Using the second equation of motion,
s=ut12gt2
s=14.7×1.50.5×9.8×(1.5)2
s11 m

For first 2 s of motion:
Using the second equation of motion,
s=ut12gt2
s=14.7×20.5×9.8×(2)2
s=9.8 m

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