Question

A car moving along a straight road with speed of 144 km h^-1 is brought to a stop within a distance of 200 m. How long does it take for the car to stop?

• A. 5 s
• B. 10 s
• C. 15 s
• D. 20 s

Answer 1

Answer: (B)

10 s

Answer 2

Here , u = 144 km $\mathrm { h } ^ { - 1 }$ $= 144 \times \frac { 5 } { 18 } \mathrm {~ms} ^ { - 1 } = 40 \mathrm {~ms} ^ { - 1 }$

V = 0, s = 200 am

As $v ^ { 2 } - u ^ { 2 } = 2 a s$

$( 0 ) ^ { 2 } - ( 40 ) ^ { 2 } = 2 \times \mathrm { a } \times ( 200 )$

$\mathrm { a } = - \frac { ( 40 ) ^ { 2 } } { 2 \times 200 } = - 4 \mathrm {~ms} ^ { - 2 }$

As v = u + at

$\therefore$0 = 40 – (4) (t)

$\mathrm { t } = \frac { 40 } { 4 } = 10 \mathrm {~s}$