Question

Please help me with the following problem:

Joe is on a cross-country trip from New York to Los Angeles. He drives for 45.0 min at 70.0 km/h, 10.0 min at 95 km/h, and 30.0 min at 55.0 km/h, and he spends 20.0 min eating lunch and buying gas. What is the average speed for this part of his trip?
a. 67.6 km/h

b. 68.4 km/h - I did b as a guess, because I couldn't figure the answer, but I got it wrong

c. 54.7 km/h

d. 53.8 km/h

Two things that I did to help me were:

Delta d
--------
Delta t

and

m - m
-------
s - s

distance is m - m is meters
time is s - seconds

For the second one I did kilometer over hour.

I have no idea on how to do this, and I have no idea of if I am doing it right or not. I have tried distance over time tons of times, and I get different answers than the ones above. Can you guys help me please? I will greatly appreciate it.

Answer 1

average velocity=distance/time

distance=3/4*70+1/6*95 + 1/2*55
time= (45+10+30)/60

check my thinking. I get none of the answers.

Answer 2

Okay, I get what you did, but is there other ways of doing this?

Answer 3

Also, why did you convert the minutes into seconds, but in fraction form?

The home-school lesson did not teach me how to do that. I don't understand why you would turn it into a fraction, can you explain it to me?

Answer 4

3/4 = .75 hour at 70 ---> 52.5
1/6 = .167 hr at 95 ---> 15.8
1/2 = .5 hr at 55 ---> 27.5
20/60 = .333 hr at 0 --> 0
total time = 1.75 hours
total distance = 95.8 km
so
95.8 km / 1.75 hr = 54.7 km/hour

Answer 5

Thank you, I now understand it.