Easy physics question (1 Viewer)

[Crosswinds]

"A cross country runner runs at 3.2 ms^-1 for 5 minutes north, then runs at 4 ms^-1 for 10 minutes north. He then returns to the start at a steady pace, taking 20 minutes. Find:
b) his diplacement after 10 minutes.
e) his average speed for the whole journey."

According to the answers:
b) 3360 m north
e) 3.2 ms^-1


But i keep getting:
b) 2160 m north
e) 192 ms^-1 (lol)

I know these are really easy, but I'm obviously doing something stupid. Could someone please explain fully how to get the correct answers?

Thank you!

 

[shady145]

no your not doing anything stupid.
ur answers are correct, xcept i got 3.4m/s for part b.

it seems the answer for (a) has the maximum displacement for the journey
and the other answer i have no idea

 

[kkyle]

Are you sure it is after 10 minutes, the answer gives you the displacement after 15 minutes.

a) 2160m
b) 3.2 ms^-1, where it is 6720/2100 = 3.2ms^-1

 

[Crosswinds]

Yep definately after ten minutes. Answers are probably wrong then.

Lol okay I did do something stupid for the second part - I forgot to change the time to seconds.

Thank you both!