 #1
 1,380
 22
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}=(1711.33)+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]
Attachments

42.6 KB Views: 266
Last edited by a moderator: