Question

Start from 110 feet away, a person on a bicycle rides towards a checkpoint and then passes it. The rider is travelling at a constant rate of 30 feet per second. The distance between the bicycle and the checkpoint is given by the equation d=|110-30t| at what times is the bike 40 feet away from the checkpoint?

a. 2.3 sec and 5 sec
b. 1.6 sec and 5 sec
c. 2.3 sec and 4.6 sec
d. 1.6 sec and 4.6 sec

Answer 1

a. 2.3 sec and 5 sec

Explanation:

The graph is symmetrical about the time (t) that makes d=0. That makes the line of symmetry be ...

110/30 = t ≈ 3.67

This will be the average of the two times, so their sum is ...

t1 +t2 = 2×3.67 = 7.3

Only one answer choice has a sum of 7.3 seconds:

2.3 sec and 5 sec