A car goes from 80 km/h to 20 km/h in 0.5 h. What is the acceleration in km/h squared?

In physics, acceleration is defined as the rate of change of the velocity of an object with respect to time. That is A = VF - VI / T;

Where A = Acceleration

VF = Final velocity = 20 km

VI = Initial velocity = 80 km

T = Time = 0.5 hr

A = (20 - 80) / 0.5 = - 60/.5

A = - 120 Km / hr^2

Therefore, the acceleration of the car is - 120 km/hr^2.

Because the value is negative, the appropriate name that describe it is deceleration.