Physics help?

Question

A race car driver must average 204.0 km/h over the course of a time trial lasting ten laps. If the first nine laps were done at 200.0 km/h, what average speed must be maintained for the last lap? (Answer to the nearest km/h.)


for all you math geniuses, its not 240 km/hr you have to manipulate the means or something

A race car driver must average 204.0 km/h over the course of a time trial lasting ten laps. If the first nine laps were done at 200.0 km/h, what average speed must be maintained for the last lap? (Answer to the nearest km/h.)


for all you math geniuses, its not 240 km/hr you have to manipulate the means or something

well i went to my teacher and said shouldnt this be 240 and he said nope your thinking about it mathematically you need to think about it physically so i did but well i'm stumped so i'd appreciate it that if you don't have any answers you'd gett off my dick. god leave it to some women to answer a science question wrong why don't you all go back to the relationships and hairstlye questions

well i went to my teacher and said shouldnt this be 240 and he said nope your thinking about it mathematically you need to think about it physically so i did but well i'm stumped so i'd appreciate it that if you don't have any answers you'd leave me alone. god leave it to some women to answer a science question wrong why don't you all go back to the relationships and hairstlye questions

thank you two for showing me the right answers physically and mathematically. See what happens when you leave the science to the men?

I tried it myself, i went to the teacher, i tried it myself again. Thats hardly lazy at all.
Then I went to yahoo answers seeking further help.
I went looking for solutions and then all women do is complain at the problem rather than offer any real answers. And you got the question wrong even after I told you that it was not that. When my someone tells me definitively that it is not a certain answer, I don't do the same thing as them trying to get the right answer. One definition of stupidity is consitently doing the same thing wrong and expecting a different result. I told you it wasn't 240 and you did the same thing as everyone else and got the same wrong answer after i told you it was wrong

Answer 1

Other responders - the answer isn't 240 km/ h because you must average velocities over equal times, not over equal distances.

Let L be the length of one lap.

To average 204.0 km / h, the car must cover 10 L in some time T1.

T1 = 10 L / 204.

The first nine laps were at 200.0 km / h so

T2 = 9 L / 200

The car has T1 - T2 time remaining to cover 1 lap, so

V = L / ( T1 - T2 )
V = L / ( 10L / 204 - 9L / 200 )
V = 1 / ( 10 / 204 - 9 / 200 )

V = 248.8 km / h

So the car must travel at 248.8 km / h on the last lap to make the desired average.

Answer 2

Well here's what this "manipulation" consists of. It is correct that the answer is not 240 km/hr because average speed is distance/time. But obviously you cannot take time for granted in any way because the 10th lap must take less time than the first nine since you go at a higher speed. So to solve for the 10th lap's speed one must solve this equation:

10D/(9D/200 + D/V) = 204.0 km/h where D is the length of the lap and V is the speed in the final lap. As you can see in the denominator distance is being divided by speed producing time and the numerator divided by the total time must equal the average speed.

To solve for V first some variables are eliminated. D is found in both the numerator and the denominator. It is simpler that:

10/(9/200+1/V) = 204.0 km/h

Next, simply cross multiplication results in:

10 = (204/200)9 + 204/V

Thus 204/V = 10 - (204/200)9

and V = 204/(10-(204/200)9)

Solving this equation brings the speed of the final lap to: 248.8 km/h.

Answer 3

Let L be the length of each Lap and let T be the total time alloted so that 10L = 204 x T

Now 9L has consumed a higher amount of time T1 = 9L/200 hours leaving 10L/204 - 9L/200 as the time available. In that time, the distance of L has to be covered. Thus the velocity is L/T2 where T2 = 10L / 204 - 9L / 200

T2 = L ( 10 x 200 - 9 x 204 ) / (200 x 204)

= L ( 2000 - 1836 ) / 40800 = 164 L / 40800

Velocity = L x 40800 / 164 L = 40800 / 164

= 248.78 km/h = 249 km/hr

Answer 4

do your homework yourself

I am so tired of kids being so lazy that they won't do their own homework. How are you going to learn it if we just give you the answer? If you don't understand it well enough to do it than ask you teacher for tutoring or extra help.

Edit- I wondered why he doesn't think it is 240 too...that's what I calculated it to be.

Further Edit- leave it to "some women" to answer the question wrong....HELLO who is the idiot asking us all the question??? Guess we can say leave it to "some guy" to be too LAZY to try and figure it out for himself and too STUPID to come up with the right answer too.

Answer 5

Ok, so you make the equation..... 200(.9) + x(.1) = 204

which becomes...

180 + .1x = 204

which becomes...

.1x = 24

which becomes...

240km/h

So, yes, for all those "math geniuses" out there, the answer is 240km/h. That is, if you want to get the answer right.

Answer 6

the answer is 240. why do you think its not??? jus curious??

Answer 7

Well why don't you go and manipulate the means then??