Answer:
Average speed v = 24.29 mph
Total time taken ∆t = 7 hours
Step-by-step explanation:
Given;
the first 2 hours, they travel at a rate of 25 miles per hour
t1 = 2 hours
v1 = 25 mph
then take a break for 2 hours and do not travel during that time
t2 = 2 hours
v2 = 0
They finally travel again for another 3 hours at a rate of 40 miles per hour before stopping for the day.
t3 = 3 hours
v3 = 40 mph
Total time taken ∆t = sum of time taken for the day travel
∆t = t1 + t2 + t3
Substituting the values;
∆t = 2 + 2 + 3 = 7 hours
The average speed v = total distance travelled/total time taken
v = d/∆t .......1
Total distance travelled d = Σ(velocity × time)
d = v1t1 + v2t2 + v3t3
d = 25 × 2 + 0×2 + 40 × 3
d = 50 + 0 + 120
d = 170 miles
Substituting into equation 1.
v = 170 miles ÷ 7 hours
Average speed v = 24.29 mph
