To find the retardation (also known as deceleration or acceleration in the opposite direction), we can use the following formula:
retardation = (final velocity - initial velocity) / time
Given: Initial velocity (u) = 72 km/hr Final velocity (v) = 0 km/hr (as the car comes to rest) Time (t) = 5 seconds
First, let's convert the initial velocity from km/hr to m/s: 72 km/hr * (1000 m / 1 km) * (1 hr / 3600 s) = 20 m/s
Using the formula: retardation = (0 m/s - 20 m/s) / 5 s retardation = -20 m/s / 5 s retardation = -4 m/s²
The negative sign indicates that the retardation is in the opposite direction to the initial velocity (deceleration). Therefore, the retardation of the car is 4 m/s².