(i) Retardation is the term used for negative acceleration.

Explanation: If the velocity of an object is decreasing, it is said to have negative acceleration.

(ii) A bus starting from rest attains a velocity of 54 km/h in 60 s, its acceleration is 0.25 m/s².

Explanation: initial velocity = 0

time = 60 secs

final velocity = 54 km/hr = m/s = 15 m/s

Acceleration =

=

= = 0.25 m/s²