## Physics (10th Edition)

Published by Wiley

# Chapter 9 - Rotational Dynamics - Problems - Page 244: 14

#### Answer

a) The force exerted by the ground on the front wheels is $1.57\times10^4N$ b) The force exerted by the ground on the rear wheels is $5.74\times10^4N$

#### Work Step by Step

The forces that act on the truck is - The weight of the truck and its contents $W=(7460kg)\times(9.8m/s^2)=7.31\times10^4N$, pointing downward. - Normal force exerted on front wheels $N_f$, pointing upward. - Normal force exerted on rear wheels $N_r$, pointing upward. Choose the rotation axis to be at the rear wheels, so that $N_r$ creates no torque. - For $W$, the lever arm is $0.63m$, and $\tau_W\lt0$ because the torque created is clockwise. - For $N_f$, the lever arm is $0.63+2.3=2.93m$, and $\tau_f\gt0$ because the torque created is counterclockwise. Because the truck is in equilibrium, 1) The net torque is zero: $$\tau_f-\tau_W=0$$ $$2.93N_f-0.63W=0$$ $$N_f=\frac{0.63W}{2.93}=1.57\times10^4N$$ 2) The net force is zero: $$N_f+N_r-W=0$$ $$N_r=W-N_f=5.74\times10^4N$$

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