Question

a car travels 30 miles at an average speed of 60miles per hour, and then 30 miles at an average speed of30 miles per hour. what is the average speed of the car over the 60 miles?

Answer 1

We know that,

Average Speed = total distance/ time taken to travel that distance

                         = (S1+S2)/(t1+t2)

                         = (30 miles + 30 miles)/(t1+t2)

                         = (60 miles)/(t1+t2)----- (1)

• Calculating t1(time taken to travel first 30 miles),

    velocity = distance/time

    time = distance/velocity---- (2)

         $t1 = 30 miles/ 60 miles per hour \\ t1 = 0.5 hours$------(a)

• Calculating t2(time taken to travel second 30 miles),

       using equation (2)

         $t2 = 30 miles/ 30 miles per hour\\ t2 = 1 hour$------ (b)

Substituting (a) and (b) values into the equation (1),

     Average Speed = 60/(0.5+1)

                                =60/1.5

                                 = 40 miles per hour

Answer :average speed of the car over the 60 miles =40 miles per hour

Answer 2

Answer:

Explanation:

We know that,Average speed when two different speeds are given is given by:

2xy/(x+y),where x and y are the two speeds.

So,answer is: 2*60*30/(60+30)=40miles per hour

Hope you understood