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A car decelerates uniformly from 20 m per second to rest in 4 seconds. The retardation is:
A5 m per second squared
B4 m per second squared
C10 m per second squared
D20 m per second squared
Answer & Solution
Correct answer: A. 5 m per second squared
1. Retardation is the magnitude of negative acceleration.
2. Use v = u + at with u = 20, v = 0, t = 4.
3. So 0 = 20 + a × 4, giving a = −5 m per second squared.
4. The minus sign means deceleration; the magnitude (retardation) is 5 m per second squared.
5. Hence the retardation is 5 m per second squared.
_Source: Selina Concise Physics ICSE Class 9, Ch 2 'Motion in One Dimension' (aplustopper.com extract)_
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