I haven't taken a physics course yet, this is for independent study, so I don't have the strongest understanding quite yet. I was wondering if I could get some insight to this problem:
Susie has planned a trip to a city 60 miles away.
She wishes to have an average speed of 60 mph for the trip.
Due to a traffic jam, however, she only averaged 30 mph for the first 30 miles.
How fast does she need to go for the remaining 30 miles so that her average speed if 60 mph for the whole trip?
1) 60 mph
2) 90 mph
3) 120 mph
D) None of the above
Average speed = change in distance / change in time
The Attempt at a Solution
If she averaged 30 mph for the first 30 miles, I want to say that if she traveled at 90 mph for the remaining 30, she would average 60 mph for the whole trip.
(30 mph + 90 mph) / 2 = 60 mph.
However, the solution is said to be none of the above. Would anyone mind explaining this?