What is the average speed for this lap?

[Janelle]

ok, i am new at physics, so please no one make fun of me for my stupid questions. Ok here is the questions
In the Canadian Grand Prix Auto race, the drivers travel a total distance of 304.3km in the 69 laps around the track. If the fastest lap time was 84.12s, what is the average speed for this lap? express your answer in metres pers second and kilometres per hour.
Please someone help me, i have a test and i need some serious help!

 

[hotvette]

You probably have an equation in your book or from your instructor that says speed_{avg} = \Delta distance / \Delta time. You know the delta time for the lap, all you need is the distance of one lap. You can calculate that from the information in the problem statement.

 

[Janelle]

do i have to change the 304.3km to metres?? and then do i divide that by 69 laps??

 

[Janelle]

do you have msn or something so i can talk to you easier hotvette??

 

[hotvette]

Yep. If you ran a 1 km race around a circular track and it took 4 laps to do so, what is the distance around the track?

 

[Janelle]

i don't understand what you are talking about. did you not just say the track was 1km?? i don't understand

 

[lawtonfogle]

Yep. If you ran a 1 km race around a circular track and it took 4 laps to do so, what is the distance around the track?

You ran 1km in four laps.

How many km per laps are there.

\frac {1km} {4 laps}

equals

.25 \frac {km } {lap}

So one lap is then .25 kms. You need to do the same with the original.

 

[hotvette]

i don't understand what you are talking about. did you not just say the track was 1km?? i don't understand

Just trying to illustrate by example. lawtonfogle explained it.

 

[lawtonfogle]

I have a 2 meter string. I rap it around a big pole two times. What is the curcumfrence of the pole?

I have a 1 meter string which I rap around a can 10 times, what is the circumfrence of the can?

I rap a 3 inch piece of string around a stick 4 times, what is the circumfrence of the stick?

 

[lawtonfogle]

Try those, so you can understand the concept.

The first one is 1 meter circumfrence.
The second one is .1 meter circumfrence.
The third one is 3/4 inch circumfrence.

 

[Janelle]

thanks guys

 

[Janelle]

i know i must be really stupid but i still don't understand, ok so i take thte 304.3km and divide it by 69 to figure hot long it takes to do one lap, but i first convert the 304.3km to metres which is 304300m, then i divide by 69, which is 4410..what units is that, do i have to do anything else..??

 

[Diane_]

Keep track of your units through the problem, Janelle.

304.3 km/69 laps = 4.410 km/lap

So that's the number of kilometers in a lap. If you change it to meters:

4.410 km/lap * 1000 m/km = 4410 m/lap

The units work algebraically, just as you learned back in Algebra 1.

And please don't worry about asking stupid questions. There are such things in the world, but you haven't even come close.

 

[Moonbear]

i know i must be really stupid but i still don't understand, ok so i take thte 304.3km and divide it by 69 to figure hot long it takes to do one lap, but i first convert the 304.3km to metres which is 304300m, then i divide by 69, which is 4410..what units is that, do i have to do anything else..??

Janelle, it doesn't matter if you do all your unit conversions in the beginning or at the end. What is important is that you are consistent with your units throughout. In other words, if you're more comfortable with km rather than meters, make sure everything that goes into your equation with some sort of distance unit is in km. At the end, if you have to give your answer in meters, you can convert km to meters then. The only rule is you can't use two different units in the same equation. So, if you needed to include two distances, you can't have one in meters and the other in km.