The friction of the air causes a vertical retardation equal to 10% of the acceleration due to gravity (take g=10 ms⁻²). The maximum height will be decreased by

Options

(a) 8%
(b) 9%
(c) 10%
(d) 11%

Correct Answer:

9%

Explanation:

Retardation due to friction of air = 8/10. Hence, in upward motion
Total retardation = g + (8/10) = 11g / 10
.·. H(m) = u² sin² θ / 2g
H(m)’ = u² sin² θ / 2×(11g/10) = (10/11)×(u² sin² θ / 2g) = (10/11) H(m)
.·. % decreases in H(m) = {[H(m) – H(m)’] / H(m)} × 100
= [1 – (10/11)] × 100 = 9%