Question

Two cars travel westward along a straight highway, one at a constant velocity of 85 km/hr, and the other at a constant velocity of 115 km/hr.

a) Sketch the velocity vs. time graph for both cars and paste your sketch in the space below.



b) Assuming both cars start at the same point, how much sooner does the faster car arrive at a destination 16 km away?

c)How far must the cars travel for the faster car to arrive 15 min before the slower car?

Answer 1

b. d1 = 85t1 = 16 km,
85t1 = 16,
t1 = 16 / 85 = 0.1882 h = 11.29 min.

d2 = 115t2 = 16 km,
115t2 = 16,
t2 = 16 / 115 = 0.139 h = 8.35 min.

t1 - t2 = 11.29 - 8.35 = 2.94 min.
Car #2 arrives 2.94 min. sooner.

c. 15 min = 1/4 h = 0.25 h.
d1 = d2,
115t = 85(t + 0.25),
115t = 85t + 21.25,
115t - 85t = 21.25,
30t = 21.25,
t = 21.25 / 30 = 0.71 h,

d = 115 * 0.71 = 81.65 km.

Answer 2

Which car was travelling at steady speed