JAMB Physics 2013 Paper

Concept:When an elevator moves downward with acceleration, the scale reading or apparent weight becomes smaller than the true weight.The difference between these two values is the apparent weight loss.Explanation:The man's true weight is $W = mg$.Substitute $m = 70\,kg$ and $g = 10\,ms^{-2}$:$W = 70 \times 10 = 700\,N$.For a downward acceleration $a = 1.5\,ms^{-2}$, the apparent weight is given by $R = m(g - a)$.$R = 70(10 - 1.5)$$R = 70 \times 8.5 = 595\,N$.Therefore, apparent weight loss = true weight $-$ apparent weight:$700\,N - 595\,N = 105\,N$.Equivalently, apparent weight loss $= ma = 70 \times 1.5 = 105\,N$.Answer:D. $105\,N$