What Forces Act on a Motorcyclist Accelerating Up an Incline?

[dorkymichelle]

Homework Statement

A motorcycle and 60.6 kg rider accelerate at 3.5 m/s2 up a ramp inclined 7.3° above the horizontal. What are the magnitude of (a) the net force on the rider and (b) the force on the rider from the motorcycle?

Homework Equations

F=ma
Fg= mg

3. The Attempt at a Solution


I'm going to use F1 = force that is making the rider go up, which is exerted from the motorcycle ?
F2 is component of gravity that opposes the motorcycle from going up.

so netforce = F1-F2
F= ma
F1-F2=ma
F2 = sin 7.3degrees = y/mg
F2 = sin 7.3degrees = y/60.6*9.8
F2=75.46
using F1-F2 = ma
I got
F1-75.46 = 60.6*3.5
F1-75.46 = 212.1
F1 = 287.56
So force that motorcycle exerts on rider is 287.56 N, since that is what's making the rider and motorcycle go up.
I also think that the net force is 287.56 because you have gravity and normal force that cancels out, then you have F1 and F2 and F1-F2 = 287.56 N
I think where I went wrong is not putting in the mass of the motorcycle, but I'm not sure how to find that?

 

[tiny-tim]

welcome to pf!

hi dorkymichelle! welcome to pf!

(have a degree: ° and try using the X₂ icon just above the Reply box )

A motorcycle and 60.6 kg rider accelerate at 3.5 m/s2 up a ramp inclined 7.3° above the horizontal. What are the magnitude of (a) the net force on the rider and (b) the force on the rider from the motorcycle?

i think you're misunderstanding the question …

there are two forces on the rider, the weight mg, and the reaction force R from the motorcycle (which is the answer to (b)) …

the net force is the sum of those two forces (as vectors, of course)

 

[dorkymichelle]

Hmm.. what do you mean weight mg, the weight of the rider or the weight of the motorcycle?

 

[tiny-tim]

hi dorkymichelle!

(just got up :zzz: …)

there are two forces on the rider, the weight mg, and the reaction force R from the motorcycle (which is the answer to (b)) …

Hmm.. what do you mean weight mg, the weight of the rider or the weight of the motorcycle?

we're only considering the forces on the rider,

so it has to be the weight of the rider

(for F = ma, or for a vector triangle, or for a free body diagram, we always use all the forces on one body only)