Simple constant velocity question

[cherryrocket]

7. Q: "If you must average 60 km/h for a 90 km trip, and you only average 40 km/h for the first 40 km, what velocity must you average the rest of the way?"

A:

90 km 60km/h 1.5h
d v t

1st
40 km 40 km/s 1h
d v t

2nd
50 km ? 0.5h (1.5-1h = 0.5h)
d v t

v = d/t = 50km/0.5h = 100 km/h

Is this the right answer and is it the right way of solving it?

 

[learningphysics]

Yes, looks right to me.

 

[m2003]

Yes, this is the correct answer and the right way of solving the problem. In order to average 60 km/h for a 90 km trip, the remaining 50 km must be covered in 0.5 hours. This means that the average velocity for the second half of the trip must be 100 km/h. This can be calculated by dividing the distance (50 km) by the time (0.5 hours). Therefore, in order to average 60 km/h for the entire trip, the remaining distance must be covered at an average velocity of 100 km/h.