Physics problem to solve

Physics
Tutor: None Selected Time limit: 1 Day

A car travels along a straight line at a constant speed of 60.0mile/h for a distance d and then another distance d in the same direction at another constant speed.The average speed for the entire trip is 30.0mile/h.A)What is the constant speed with which the car moved during the second distance d?B)What If? Suppose the second distance d were traveled in the opposite direction;> 

Oct 21st, 2015

Hello!

A) The average speed is the total distance travelled divided by the total time.

The total distance is 2d.

Denote the second speed as v. Then the total time is (d/60 + d/v).

So we obtain equation (2d)/(d/60 + d/v) = 30. d factors out,

2/(1/60 + 1/v) = 30, or 1/60 + 1/v = 1/15, or

1/v = 1/15 - 1/60 = 3/60 = 1/20, v = 20 (mile/h)

B) the question is incomplete, please clarify.

Please ask if something is unclear.
Oct 21st, 2015

Oh sorry, here is the B question: b) What If?  Suppose the second distance d were traveled in the opposite direction;  You forgot something and had to return home at the same constant speed as found in part (a).  What is the average velocity for this trip?  (c) What is the average speed for this new trip?

Oct 21st, 2015

And C also:)

C) the average speed remains the same because distance travelled is still 2d.

B) if the average velocity is defined as (displacement)/(time), then it will be zero, because the displacement is zero (we returned to the initial point).

Oct 21st, 2015

Thanks a lot!

Oct 21st, 2015

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