Question 9
An object of mass 4 kg is moving at uniform velocity. A force of 6 N is applied to it in the direction opposite to its motion. What retardation is produced?
The right answer is the one marked above.
A retardation of 1.5 m s−2. The magnitude is found exactly as before:
a = F ÷ m = 6 N ÷ 4 kg = 1.5 m s−2
But the force opposes the motion, so the acceleration does too — that is, −1.5 m s−2. A negative acceleration is a retardation, of magnitude 1.5 m s−2.
Had the same force been applied along the motion, the acceleration would be +1.5 m s−2. The number is identical; only the sign changes.