Question

A bus moving along a straight highway with speed of 72 km/h is brought to halt within 4s after applying the brakes. The distance travelled by the bus during this time (Assume the retardation is uniform) is _______m.

Answer 1

1. Convert Initial Velocity to m/s:
The initial velocity $u = 72 \, \text{km/h}$ can be converted to m/s:
$u = 72 \times \frac{1000}{3600} = 20 \, \text{m/s}.$

2. Use Equation of Motion to Find Retardation:
Using $v = u + at$ with final velocity $v = 0$, time $t = 4 \, \text{s}$:
$0 = 20 + a \times 4.$ Solving for $a$:
$a = -5 \, \text{m/s}^2.$

3. Calculate Distance Using $v^2 - u^2 = 2as$:
Substitute values:
$0^2 - 20^2 = 2 \times (-5) \times s.$ Simplifying:
$s = 40 \, \text{m}.$

Answer: 40 m