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

jakeharris02
Jan 3, 2018

#1**+1 **

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

CPhill
Jan 3, 2018