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## Homework Statement

A car of weight 17[kN] starts to move. the coefficient of friction is 0.6. the dimensions in the drawing.

The height of the CoM, point C, is 0.5[m]. the front wheels drive the car.

What are the pressing forces on the front and rear wheels and what is the friction force on the front wheels.

## Homework Equations

Friction: f=μN

Moments: F

_{1}L

_{1}=F

_{2}L

_{2}

## The Attempt at a Solution

R

_{f}is the reaction on the front and R

_{r}is on the back. the reactions caused by the weight:

$$R_f=\frac{2}{3}\cdot 17=11.33$$

The friction force on the front: f=0.6⋅11.33=6.8. it should be 4.36.

The friction "pulls the carpet" under the CoM and creates a moment which is balanced by the rear wheels:

$$0.5\cdot 6.8=R_r\cdot 2\rightarrow R_r=1.7$$

This force adds to the reaction to the weight: R

_{r}=(17-11.33)+1.7=7.37

Of course it's not true. it should be R

_{r}=4.47. the pressing force on the front wheels should be R

_{f}=7.27

But the motor reacts to the torque applied to the front wheel and this moment increases the pressure on the rear wheels, but for that i need the radius of the wheel.[/SUB]

[Moderator note: repaired subscripting tags - gneill]

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