A car moving with a speed of 40 km/h can be stopped by applying brakes after at least 2m. If the same car is moving with a speed of 80 km/ h. The minimum stopping distance will be……………..

Options

A. 8
B. 2
C. 4
D. 6

Answer

A

Explanation

Stopping distance `ds = (v ^(2))/(2d) " "…(1)`
Here, `v _(1) = 40 km//h = 40 xx (5)/(18) = 11 m //s and ds _(1) = 2m` is given.
`therefore 2 = ((11) ^(2))/( 2a _(1))` (From eq. (i))
`therefore 4a =121`
`therefore a _(1) = 30 ms ^(-1)`
Now, same car is there, so `a _(1) =a_(2) =a.`
`therefore v _(2) = 80 km//h =8- xx (5)/(18) ~~22m//s and a _(1) =a_(2) =30 ms ^(-1) ,So, ds _(2) = ?`
`therefore ds _(2) = ((22) ^(2))/(2 xx 30 )= (484)/(60) `
`therefore ds _(2) = 8m`