Question

On a road trip, a driver achieved an average speed of (48.0+A) km/h for the first 86.0 km and an average speed of (43.0-B) km/h for the remaining 54.0 km. What was her average speed (in km/h) for the entire trip? Round your final answer to three significant figures.
A=16, B=8

Answer 1

you need to use the formula average speed = distance / time taken
Note you cannot average speeds because speeds are ratios.

Answer 2

first calculate the time taken for both parts of the journey using t = d / s
Then calculate the total os these 2 times then use

s = d /t = (86+54) / t

Answer 3

this will give you the average time for the entire trip

Answer 4

time for first part of the trip = 86 / (48+16) h

Answer 5

so I got about 1.34 for the first time? I think I'm doing this wrong..

Answer 6

86 / 64 hors in the time for the first part

Answer 7

Oh, so don't reduce. haha oops

Answer 8

as a decimal this is 1.344

we need to correct it to 4 significant figures because the question want the answer correct to 3 sig figs.

Answer 9

oh okay

Answer 10

yes - you can reduce because the question wants answer as decimal

Answer 11

second part, time = 54 / (43-8) = 54 / 35

Answer 12

so the second time would be 53/35? which would be 1.514 ?

Answer 13

= 1.543 i make it

Answer 14

oh yeah 54, sorry!

Answer 15

so total time = 1.344+ 1.543 = 2.887

total distance = 54 + 86 = 140

so average speed for whole journey is 140 / 2.887 km/h

Answer 16

I got 48.49 km/h

Answer 17

thats correct
which to 3 sig figs is 48.5 km/h

Answer 18

thank you so much!! :)

Answer 19

yw