Answer to Question #329824 in Physics for dandan

Question

1. You normally drive on the freeway between Lopez, Quezon and San Pablo, Laguna at an

average speed of 105 km/hr, and the trip takes 2 hours and 20 minutes. On a Friday

afternoon, however, heavy traffic slows you down and you drive the same distance at an

average speed of only 70 km/hr. How much longer does the trip take?

Answer 1

The distance can be found as follows:

$$d = v_1 t_1$$

where $v_1=105km/h$, $t_1 = 2h\space 20min=7/3h$. The time in the second case is:

$$t_2 = \dfrac{d}{v_2} = \dfrac{v_1t_1}{v_2}$$

where $v_2 = 70 km/h$. Thus, obtain:

$$t_2 = \dfrac{105km/h\cdot 7/3h}{70km/h}=3.5h=3h\space 30 min$$

Answer. It will take 3h 30min.