Question

PLEASE HELP!
An aircraft flew a distance of 3000 km from Berlin to Cairo at an average speed of v km/h.
i) Write down an expression for time in hours what it took for the journey.
ii)The aircraft returned non-stop from by the same route at an average speed of 2v km/h.write an expression to show this.
iii)Write down an expression for the time in hours
iv)Given that the time for the journey is 4 hours, form an equation in v and solve it.
Guys i need you!

Answer 1

OK so do you know the basic equation, rate * time = distance?

Answer 2

Yes I do

Answer 3

OK, so for part (i), plus in the rate and the distance, then isolate t.

Answer 4

Is it: t=3000/v?

Answer 5

yep, exactly

Answer 6

Now the same for (ii)

Answer 7

so 3000/2v?

Answer 8

yep

Answer 9

Now you have written two expressions for the time out and the time back. So if you know the total time for the round trip is 4 hours, can you express that as an equation?

Answer 10

uhm....4=3000/3v ?

Answer 11

no, you can't combine unlike denominators. It's just 4 = (the sum of your two previous expressions)

Answer 12

4=6000/v? This is where i start gettin a bit confused

Answer 13

it's really simple, just literally put a plus sign between the two expressions you computed in part (i) and part (ii)

Answer 14

Are you saying: 4=3000/v+3000/2v?

Answer 15

right

Answer 16

just to be clear, it's
\[4 = {3000 \over v} + {2000 \over 2v} \]

Answer 17

Now to solve you multiply the whole thing through by 2v, which means multiplying each term by 2v.

Answer 18

So 4*2v=2v*3000/v+2v*3000/2v

Answer 19

right, now cancel out the extra v's, what do you get?

Answer 20

you should get an equation with no division in it any more

Answer 21

2v*4=v3000+3000

Answer 22

exactly! now collect the v's on one side

Answer 23

2v-3000v=3000/4

Answer 24

hmm, something is fishy here, let me try and figure out what went wrong

Answer 25

OK

Answer 26

ack, ok, haha

Answer 27

So if you have 4 = (3000/v) + (3000/2v) and you multiply by v, all the v's on the right cancel.

you get 4 * 2v = 2v*(3000/v) + 2v*(3000/2v)

Answer 28

All the v's cancel out of the right side.

Answer 29

I keep getting 2v*4=3000v+3000 as when the 2v is * by the 3000/v I would end up with that.

Answer 30

By the way thanks for the help so far