how fast must a train travel the second mile of a two mile journey to average a speed of 60 mph?

Question

for the whole journey if it has just completed the first mile at an average speed of 30 mph

Answer 1

Impossible.

Variance is Time. To get the average of 60 mph for 2 milels journey, you must know the time.
2 miles/time= 60 mph
time = 2/60 *60 = 2 mins
since at 1st mile the train has traveled at 30mph. It has already spent 2 mins. So, it's not possible to get average of 60mph.

Answer 2

Using the theory of relativity the train will need to travel at the speed of light on the second half of the journey to be able to average 60 mph as it will take 2 hours to do the first leg and need to do the second leg in no time at all.

The only way to do that is to travel at light speed.

Answer 3

the train is only allowed 2 minutes to run
the 2 miles in order to average 60 mph
in the first mile,the train has already
used up it's 2 minutes-it therefore
has to travel the second mile in zero
time-as speed is relative this is impossible
even if the train travelled at the speed of
light for the second mile,the average speed
would still be less than 60 mph

it's rather like saying that a straight line is
a circle with infinite radius-it is undefined

i hope that this helps

Answer 4

Trick question... it's impossible to average 60mph over two miles.

The first mile the train averaged 30mph. With rt=d, the time for the first mile is 1/30 of an hour, or 2 minutes.

For the train to average 60mph over the two miles, again using rt=d, the time for the entire trip must be 2/60 of an hour, or 2 minutes. The full time needed to make the 2-mile trip was already exhausted in the first mile.

Answer 5

It is impossible for the train to average 60 MPH, for it would have to go 2 miles in 2 minutes to do so, but spent the full 2 minutes going 1 mile

Answer 6

It is not possible because the time required to attain
V(ave) =60 mph is already consumed by travelling the first mile at 30 mph. That is, train will have to reach infinite speed at 0 seconds to make it happen.

Answer 7

The answer is: NOT POSSIBLE

To average 60 MPH for a 2-mile trip, the total trip must take 2 minutes. (Because 60 mph = 1 mile per minute, so 2 minutes for 2 miles = 60 MPH average.)

But notice that if your average MPH for the first mile is 30 mph, then that means you spent 2 minutes going the first mile. (Because 30 MPH = 1/2 mile per minute, so 1 mile requires 2 minutes of travel time.)

But, since at the end of 2 minutes you've only gone 1 mile, and you need to spend 2 minutes total going the whole 2 miles to average 60 MPH for the whole trip, you would need to spend ZERO amount of time on your second mile, which is not possible.

Therefore it's not possible to attain an average speed of 60 MPH for the 2-mile trip if you average 30 MPH during the first mile.

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EDITED TO ADD: I initially said the answer was 90, but after seeing the disparity of answers here, it made me double check my work and I see that my initial answer was wrong. Editing my answer only to provide the asker with the correct information. Please give best answer to one of the folks below who said the answer was inifinity or speed of light or not possible (such as Shauna or BMW).

Answer 8

1st mile = 30 mph => time taken =1/30 hrs = 2 mins n avg speed for 2 miles = 60mph => total time = 2/60 hrs = 2 mins But the 2 mins r already taken up for the first mile so it is not possible to average out 60 mph for 2 miles in this case

Answer 9

The answer is INFINITITY. Now for the Rocket Science. To do a two mile journey at an avarage speed of 60mph you need to be 2 minutes on the track. But if you did half the distance at 30mph you have used up all your time 'cause it takes 2 minutes to do 1 mile at 30mph. So you need to do the second mile in zero time

Answer 10

To solve these average speed questions you need to use the harmonic mean. In this case -

1/30 + 1/x = 2/60

Multiply all through by 60x to get

2x + 60 = 2x

No value of x will make this equation true.