When brakes are applied to a bus, the retardation produced is 25 cm s-2 and the bus takes 20 s to stop. Calculate – (i) the initial velocity of bus, and (ii) the distance travelled by bus during this time.

v = u + at

Given,

Retardation = -a = -25 cm s^-2

Hence, -a = -0.25 m s^-2

t = 20 s

v = 0

u = ?

Substituting the values in the formula above we get,

0 = u + (-0.25) × 20

or, 0 = u – 5

or, u = 5 ms^-1

Hence, the initial velocity of bus = 5 m s^-1

(ii) As we know, from the equation of motion,

v² = u² + 2aS

Substituting the values, we get,

0² = 5² + 2 × (-0.25) × S

or, 0 = 25 – 0.50 × S

or, 0.50 × S = 25

or, S = 25/0.5 = 50 m

Hence, distance travelled = 50 m