Question 3
The velocity of an object moving along a straight path falls uniformly from 12 m s-1 to 0 in 4 s. Which statement about this motion is correct?
The right answer is the one marked above.
The acceleration is −3 m s-2; the retardation is 3 m s-2.
acceleration = (0 − 12) m s-1 ÷ 4 s = −3 m s-2
When the value for acceleration comes out negative, it tells us the velocity is decreasing — here by 3 m s-1 every second. A negative acceleration is called a retardation, or deceleration. So an acceleration of −3 m s-2 is a retardation of 3 m s-2.