Theory question 108
DynamicsA force of F N acts on a body of mass 50 kg and changes its velocity from 30 ms−1 to 40 ms−1 in 6 seconds. Find the: (a) magnitude of the force; (b) acceleration of the body. (c) distance covered in 9 seconds when the initial velocity is 30 ms−1. [Take g = 10 ms−2]
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Model answer
(a) F = m(v − u)/t = 50 × 10/6 = 250/3 ≈ 83.3 N.
(b) a = F/m = (40 − 30)/6 = 5/3 ≈ 1.67 ms⁻².
(c) s = ut + ½at² = 30(9) + ½(5/3)(81) = 270 + 67.5 = 337.5 m.
Explanation
In (c) use the body's acceleration, not g.