A physics question involving a tri-cycle...?

Question

A tri-cycle is at rest and the pedal is attached by a string. You pull the string with force F.
What does it do? and why? There is 4 reasons (concepts to the why question) so can anyone help me?

Answer 1

The easiest way to visualize why it will always move forward is to consider cycloids, which are curves traced out by a point on the circumference of a rolling circle. At no time does this point have a retrograde motion, so therefore, if this point is within the diameter of this circle and is pulled by a string from a distance ahead of it, it will roll foward. Check wiki w/animation on the cycloid.

For geared bicycles, check the path of the point where the string is attached to the pedal. If there is no retrograde motion, it will move foward. For a counterexample, if the gear ratio is very high, so that the pedal spins several times for each rotation of the wheel, we know that pulling it with a string isn't going to work.

For a force analysis, read Alexander's reply.

Answer 2

The tri-cycle will always go in the direction,
in which you pull the string.

If the sting is atttached at the pedal currently
at bottom, the trike will go forvard anyway.

The only parameter in play (which determines
the force needed to stop the trike applied to
the frame)
is the ratio

(height of the pedal _above the ground)
----------------- ---------- -------------------- -----
. . .. (radius of the front wheel)

The axis of ratation is where the front wheel
touches the ground.

Answer 3

the cycle will not move. this is because the wheel at the pedal is smaller than the wheel on the road. hence any displacement in the pedal results in a larger displacement at the road wheel and this is not allowed since the string is being pulled. so the cycle will not move.

Answer 4

you need to indicate the initial position of the pedals, and the direction the string is being pulled.

Answer 5

wheels wont turn, because the string is pulling in one direction, for the cycle to turn you need force on it from every direction.
if there is enough pulling force, it may slide.

Then you get into static friction, and sliding friction.