If a body's velocity changes from +20 m/s to –10 m/s in 4 seconds, the acceleration is _______.
– 7.5 m/s2
Acceleration is the rate of change of velocity: \(a = \dfrac{v - u}{t}\), where u is the initial velocity, v the final velocity and t the time taken.
Here the initial velocity u = +20 m/s, the final velocity v = −10 m/s and the time t = 4 s.
Substituting: \(a = \dfrac{(-10) - (+20)}{4} = \dfrac{-30}{4} = -7.5\) m/s2.
The negative sign shows the acceleration is opposite to the original direction of motion (the body is slowing down and then reversing).
Hence, the acceleration is −7.5 m/s2.
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