Time, Speed & Distance
Aptitude

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Q.

When an object is dropped, the number of feet N that it falls is given by the formula (N=dfrac{1}{2}gt^2) where t is the time in seconds from the time it was dropped and g is 32.2. If it takes 5 seconds for the object to reach the ground, how many feet does it fall during the last 2 seconds?

 A.

64.4

 B.

96.6

 C.

161.0

 D.

257.6

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Solution:
Option(D) is correct

In 5 seconds it travels

\(=\left(\dfrac{1}{2}\right)\times 32.2\times 52\)

\(=16.1\times 25\)

\(=402.5\)

In first 3 seconds it travels

\(=\left(\dfrac{1}{2}\right)\times 32.2\times 32\)

\(=16.1×9\)

\(=144.9\)

Hence in the last 2 seconds it travelled $402.5−144.9$= 257.6


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