Physics Problem

[Milk 0]

I have some physics homework tonight and I can't freaking figure out this one problem:

Emily takes a trip, driving with a constant velocity of 87.5 km/h to the north except for a 22 min rest stop. If Emily's average velocity is 72.8 km/h to the north, how long does the trip take?

I've asked a few friends and none of them know what to do...please if anyone can help me :) I would really, really appreciate it.

[Dawid 0]

Okay, this one is a little tricky but I managed to get it. What it is saying is that the person travelled at a constanst speed of 87.5km/h(no acceleration, no deceleration at all ever) and then came to an immediate stop for 22 minutes, and at the end of it all her average speed was 72.8.Now the way to work this out is to remember that firstly we are dealing with minutes, so convert 87.5km/h and 72.8km/h to minutes87.5/60=1.45633km/m(best to keep in calculator memory for accurate readings)72.8/60=1.21333km/m(best to keep in calculator memory for accurate readings)Now, basically what we are trying to find is a distance covered by the vehicle that is equal to 87.5km/h in X minutes, and 72.5km/h is X+22 minutes. She will have covered the same distance but the 22 minute break gave a slower average so we will take the time as X and X+22(for the 22 minute break).So your equation should look like thisConstantSpeed * time = AverageSpeed * time+22Thus 1.45633*x = 1.21333(x+22) 1.45633x = 1.21333x + 26.69326 0.243x = 26.69326 x = 109.848Thusx=109.85The time taken was around 109.85 minutes.You can check like this: 109.85 * 1.45633km/m = 159.99 109.85+22 * 1.21333km/m = 159.99Make sure you keep all calculations in calculator memory though and work off that to get the most accurate reading.

[kasm 0]

I have some physics homework tonight and I can't freaking figure out this one problem:

I've asked a few friends and none of them know what to do...please if anyone can help me :) I would really, really appreciate it.

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We know that t=d/v .........(1)

where d is the distance and

t is time of the journey if the object was moving with constant velocity 'v'

also in the problem the direction is one direction i.e no complication

 

We have two unknowns d and t so we will try to build 2 equation from the given information to solve the two unknowns.

 

1. the object was moving with average velocity 72.8 km/h. So by applying formula (1) we get

t = d/72.8............(2)

 

2. Emily takes a trip, driving with a constant velocity of 87.5 km/h to the north except for a 22 min rest stop

 

So by applying formula (1) but with consideration that if the velocity was 87.5 km/h the actual time will be less by the time she was resting i.e 22/60 hour [ we have to use hour because the velocity was per hour ]

 

then the second equation will be:

 

t = d/87.5 + 22/60 .........(3)

 

Solving (2) and (3) we can eliminate t and find the required 'd'

 

 

d/72.8 = d/87.5 + 22/60

d/72.8 - d/87.5 = 22/60

 

 

d [1/72.8 - 1/87.5 ]= 22/60

Then use your calculator to find 'd' the distance required to finish the solution [ I hate calculators ]

[Dawid 0]

Yeah, both will work.