Question

A body starting from rest is moving with an uniform acceleration of 8m/s^2.Then the distance travelled by it in 5th second will be....

Answer 1

Since, the body starts from rest, it's initial velocity (u) = 0

And acceleration (a) = 8m/s²

Distance travelled by it in 5th second can be found in 2 ways

One is directly using the formula

S(nth) = u + a(n - 1/2)

S(5th) = 0 + (8)(5 - 1/2) = 8(9/2) = 36m

Other way is find the distance travelled in nsec, find the distance travelled in (n-1)sec then subtract it.

Here,
S(5) - S(4) = {0 + 8 × 5²/2 } - {0 + 8 × 4²/2}

= 4 × 5² - 4 × 4²

= 4 (5² - 4²)

= 4 ( 25 - 16)

= 4 (9)

= 36m