Question

plz ans it guys plz give correct answer

Answer 1

Answer

Option 2 is correct

t = 3u/5a

Given

The velocity , u of a body moving in a straight line with a constant retardation reduces by 60 % .

To Find

Time taken to doing so

Solution

Initial velocity , u = u m/s

A/c , " The velocity , u of a body moving in a straight line with a constant retardation reduces by 60 % "

$\implies \rm v=u-60 \%\ u\\\\\implies \rm v=u-\dfrac{60}{100}u\\\\\implies \rm v=\dfrac{100u-60u}{100}\\\\\implies \rm v=\dfrac{4u}{10}\ m/s$

Acceleration , a = - a [ ∵ retardation ]

Time , t = ? s

Apply 1st equation of motion ,

$\implies \rm v=u+at\\\\\implies \rm \dfrac{4u}{10}=u+(-a)t\\\\\implies \rm \dfrac{2u}{5}=u-at\\\\\implies \rm at=u-\dfrac{2u}{5}\\\\\implies \rm at=\dfrac{(5u-2u)}{5}\\\\\implies \rm at=\dfrac{3u}{5}\\\\\implies \rm t=\dfrac{3u}{5a}$

So , option 2 is correct