中4數學1條

(a) As (t s) varies directly as the (d km), Let t = k d, where k is a constant

it takes 12seconds for you to hear the thunder from lighting that is 5km away
t = k d
12 = k (5)
k = 12/5 = 2.4

therefore, t = 2.4 d or t = (12/5)d


(b)
(1) d = 3 km
as t = 2.4 d
t = 2.4 (3)
t = 7.2

therefore, it takes 7.2 seconds for me to hear the thunder from the lighting that is 3km away

(2) d = 8 km
as t = 2.4 d
t = 2.4 (8)
t = 19.2

therefore, it takes 19.2 seconds for me to hear the thunder from the lighting that is 3km away


(c) t = 1
as t = 2.4 d
1 = 2.4 d
d = 1/2.4
d = 0.417 (correct to 3 decimal space)

therefore, the lighting is 0.417km away if the time between the thunder and lighting is only 1 second