Question

A car moving with 54 km/hr on application of brakes it stops in 8 sec . calculate the acceleration .

Answer 1

Here we've
=> u= 54 km/h , v=0 m/s , t=8 sec , a=?

Since 'u' is given in km/h we've to convert it into m/s by multiplying it with 5/18
=> 54 *(5/18) => 15 m/s

We can use the equation
=> v=u+at
=>0=15+a*2
=>a=-15/2
=>a=-7.5 m/s²

Answer 2

v = u +at
----------------------
v =0
u = 54km/hr
= 54 x 5/18
=270/18
=15 m/s

time =2 s

v = u + at

15 = 0 + a(2)

a = -15/2

=-7.5 m/s²
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-ve sign indicates that body is having deceleration