ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Physics => Topic started by: Srd2000 on January 31, 2019, 02:36:12 am

Hi All, I’ve got a rather confusing problem on my hands. I believe I’m over complicating it with velocitytime graphs and simultaneous equations, but I’m not sure.
A person walks 50km in 4hrs. They start off walking 7km at a rate of x km/h. Then they ride a bike at 4x km/h for another 7km. Lastly, they drive a car the remaining distance at (6x+3) km/h. What is the value of x km/h?
Ans: x=3.5 km/h
My intial thinking was to do a velocitytime graph and use the area as mentioned, but that fell short when I introduced t1 and t2, respective times for when the person changes their transport. Then I tried solving it simultaneously, that got a negative answer. I’m sure that I’ve just overthought it or gone down a rabbithole.
I’d much appreciate if someone could help out. Thank you!!!

Hi All, I’ve got a rather confusing problem on my hands. I believe I’m over complicating it with velocitytime graphs and simultaneous equations, but I’m not sure.
A person walks 50km in 4hrs. They start off walking 7km at a rate of x km/h. Then they ride a bike at 4x km/h for another 7km. Lastly, they drive a car the remaining distance at (6x+3) km/h. What is the value of x km/h?
Ans: x=3.5 km/h
My intial thinking was to do a velocitytime graph and use the area as mentioned, but that fell short when I introduced t1 and t2, respective times for when the person changes their transport. Then I tried solving it simultaneously, that got a negative answer. I’m sure that I’ve just overthought it or gone down a rabbithole.
I’d much appreciate if someone could help out. Thank you!!!
You know the total distance and total time. Use them.
First section: travels 7 km, 7/x hours
Second section: travels 7 km, 7/(4x) hours
Third section: 50  14 = 36 km, 36/(6x+3) hours
Add the times, set equal to 4 hours.

Oooooh, that makes sense. I kept trying to use just the distance and speed to find x while ignoring time completely. My bad, oops.
Thank you, lzxnl!