+-40 a tennis ball is thrown vertically upwards with a speed of v m/s. the height, H metres, reached by the ball is proportional to the square of v. when v = 30m/s, h = 30m work out the value of:
a) H when v = 20m/s
b) v when H = 15 m
+128473 We have this :
H = kv^2 and we need to find the proportionality constant, k.....so we have
30 = k (30)^2
30 = k (900) divide both sides by 900
(1/30) = k
So....at 20m/s, H =
(1/30)*(20)^2 = 400/30 = 40/3 ≈ 13.33 m
When H = 15m, v =
15 = (1/30) v^2 multiply both sides by 30
450 = v^2 take the positive root of both sides
sqrt (450) = v = 3sqrt(50) ≈ 21.2 m/s
