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

Correct Answer: 40

1. Initial Velocity Conversion:
Convert the initial velocity \( u = 72 \, \text{km/h} \) to meters per second:
\[ u = 72 \times \frac{1000}{3600} = 20 \, \text{m/s}. \]

2. Determine Retardation:
Apply the equation of motion \( v = u + at \), where final velocity \( v = 0 \) and time \( t = 4 \, \text{s} \):
\[ 0 = 20 + a \times 4. \] Solve for acceleration \( a \):
\[ a = -5 \, \text{m/s}^2. \]

3. Calculate Distance:
Use the equation \( v^2 - u^2 = 2as \) and substitute the known values:
\[ 0^2 - 20^2 = 2 \times (-5) \times s. \] Simplify to find the distance \( s \):
\[ s = 40 \, \text{m}. \] 

Result: 40 m