Question

| 131. A stone is thrown vertically down-
wards and the formula d = 16t ^2+
4t gives the distance, d metres,
that it falls in t seconds. How long
does it take to fall 420 metres ?​

Answer 1

Answer:

5 Seconds

Step-by-step explanation:

420 = 16t^2+4t

16t^2+4t-420=0

4(4t^2+t-105)=0

4t^2+t-105=0

(4t+21)(t-5)=0

t = 5 & t = -5.25

Time cannot be negative, therefor t = 5 seconds