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Question

A body falls freely from a tower and travels a distance of 40 in its last two seconds. The height of the tower is

A
54 m
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B
45 m
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C
80 m
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D
65 m
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Solution

The correct option is B 45 mLet the body fall through the height of the tower in t seconds. From equation of motion we have S=ut+12gt2 , here u= 0 as the body is free falling H=12gt2 Where H is the height of the tower. The distance covered by the body in t−2 seconds is H′=12g(t−2)2 Now, according to question H–H'=40 m Assuming g as 10 m/s2 t2–(t–2)2=8 4(t–1)=8 t=3 seconds Now, the height of tower Therefore, option B is correct.

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