Natwerk Designs

How do I do this physics problem?

The stoplights on a street are designed to keep traffic moving at 37 mi/h. The average length of a street block between traffic lights is about 80 m. What must be the time delay between green lights on successive blocks to keep the traffic moving continuously? Answer in units of s. my second question is On a drive from your ranch to Austin, you wish to average 48 mph. The distance from your ranch to Austin is 98 miles. However, at 49 miles (half way), you find you have averaged only 36 mph. What average speed must you maintain in the remaining distance in order to have an overall average speed of 48 mph? Answer in units of mph. I know the speed and velocity formula and that the first one needs some mph to mps conversions. But I don't know how to go about doing either of them.

Public Comments

1. To convert 37 mph to m/s... 37 mi / hr x 1609 m/mi x 1 hr/3600 s = 16.5 m/s 80 m / 16.5 m/s = 4.8 sec would do it... The first half of the trip took you... t = d/v = 49 mi / 36 mph = 1.36 hr To average 48 mph would take... t = d/v = 98 mi / 48 mph = 2.04 hr Time left to finish the trip averaging 48 mph... 2.04 - 1.36 = 0.68 hr Speed to average... v = d/t = 49 mi / 0.68 hr = 72 mph Hope that helped...