Calculating Net Force on a Cyclist: Newton's Law Q Explained

[pencilcase]

A cyclist is pedaling so that a force of 100N pushes her forward while there are 50N of friction and 50 N of air resistance opposing her movement. What is the net force on the cyclist?

 

[Dick]

A cyclist is pedaling so that a force of 100N pushes her forward while there are 50N of friction and 50 N of air resistance opposing her movement. What is the net force on the cyclist?

Sounds pretty easy to me. What do you think? That's the important part.

 

[pencilcase]

i think its either 200n or 0n :/

 

[Dick]

i think its either 200n or 0n :/

That's good. So which? 100N forward. I think 'opposing her movement' should tell you which direction the other two are, yes? 'Net force' means you add the forces considering the sign of each one.

 

[pencilcase]

so its 200 n

 

[Dick]

So there is no net force on her?

Right. If she's moving 20km/hr she'll keep on moving 20km/hr until she stops working and slows down or works harder and speeds up.

 

[Dick]

so its 200 n

I liked your first answer better. If you call forward positive then the other backward forces are negative. 100N+(-50N)+(-50N)=0N.

 

[pencilcase]

ooooooh ok thanksss!