# Vehicle Dynamics MCQ – Set 2

This set of Vehicle Dynamics Multiple Choice Questions & Answers (MCQs) focuses on “Axle Loads”.

1. Air resistance loads are neglected at low vehicle speed.
a) True
b) False

Explanation: Air resistance forces depend on the square of the speed. Therefore, at low speed, the air resistance force is negligible compared to other loads such as rolling resistance and gradient loads.

2. The equation Wfs = W$$\frac{c}{L}$$ denotes ____________
a) Static load on the rear axle on a level ground
b) Dynamic load on the front axle on level ground at low speeds
c) Dynamic load on the rear axle on level ground at low speeds
d) Static load on the front axle on a level ground

Explanation: Wfs denotes the static load on the front axle. W represents the weight of the vehicle. L and c represent the wheelbase and the longitudinal distance along the base from the rear axle to the center of gravity of the car, respectively. Static load on the rear axle on level ground is given by Wrs = W$$\frac{b}{L}$$. The dynamic load on the front axle on level ground at low speeds is given by $$W_f = W \left( \frac{c}{L} – \frac{a_x}{g} \cdot \frac{h}{L} \right)$$. And on rear axle its $$W_r = W \left( \frac{b}{L} + \frac{a_x}{g} \cdot \frac{h}{L} \right)$$.

3. Which among the following has the maximum axle load considering the center of gravity of the vehicle bisects the wheelbase?
a) Static load on the rear axle on a level ground
b) Dynamic load on the front axle on level ground at low speeds
c) Dynamic load on the rear axle on level ground at low speeds
d) Static load on the front axle on a level ground

Explanation: Static load on the front axle on level ground is given by Wfs = W$$\frac{c}{L}$$. Static load on the rear axle on level ground is given by Wrs = W$$\frac{b}{L}$$. Whereas, dynamic load on the front axle on level ground at low speeds is given by $$W_f = W \left( \frac{c}{L} – \frac{a_x}{g} \cdot \frac{h}{L} \right) = W_{fs}-W \frac{a_x}{g} \frac{h}{L}$$and on rear axle its $$W_r = W \left( \frac{b}{L} + \frac{a_x}{g} \cdot \frac{h}{L} \right) = W_{rs}+W \frac{a_x}{g} \frac{h}{L}$$. As the CG bisects the wheelbase b=c and Wfs=Wrs. Hence dynamic axle load on the rear axle on level ground at low speeds is greater.

4. What is the common grade of interstate highways?
a) up to 4 percent
b) up to 10 percent
c) up to 12 percent
d) above 15 percent

Explanation: Interstate highways allow high vehicle speeds. The grade is kept below 4 percent to minimize axle loading due to the grade. 10 to 12 percent grade is occasionally reached on primary and secondary roads.

5. Axle load on the rear axle as influenced by a positive grade is given by ______
a) Wfs-W$$\frac{h}{L}$$θ
b) Wrs+W$$\frac{h}{L}$$θ
c) Wfs+W$$\frac{h}{L}$$θ
d) Wrs-W$$\frac{h}{L}$$θ

Explanation: θ represents a very small angle. The sine of the angle is very close to the angle. On a positive grade, the load gets transferred from the front to the rear axle. Hence the load on the rear axle becomes Wrs+W$$\frac{h}{L}$$θ. And, the load on the front axle becomes Wfs-W$$\frac{h}{L}$$θ.

6. What is the static load on the front axle of a 2000 kg car, with a 2 m wheelbase, where the center of gravity of the car bisects the wheelbase?
a) 500 N
b) 8000 N
c) 9810 N
d) 9180 N

Explanation: Static load on the front axle is given by Wfs=W$$\frac{c}{L}$$. Mass of car given is m=2000 kg. The wheelbase is L = 2 m. Since the center of gravity bisects the wheelbase, c = 1 m. Taking acceleration due to gravity as g=9.81m/s2. The weight of the car is W=mg=19620 N. Therefore, the static load on the front axle becomes Wfs=W$$\frac{c}{L}$$=19620⋅$$\frac{1}{2}$$=9810 N.

7. At low-speed dynamic axle load always remains constant.
a) True
b) False

Explanation: $$W_r = W \left( \frac{b}{L} + \frac{a_x}{g} \frac{h}{L} \right)$$ denotes the dynamic axle load on the rear axle at low-speeds. It is seen that it depends on the acceleration of the vehicle which is not constant.

8. While accelerating, why does the rear axle have more load than the front axle?
a) due to weight transfer
b) due to a manufacturing defect
c) due to weight imbalance
d) due to air drag

Explanation: During acceleration, there is load transfer from the front axle to the rear axle. Thus in dynamic conditions, the rear axle has more weight than during static conditions. This is evident from the equation $$W_r = W \left( \frac{b}{L} + \frac{a_x}{g} \frac{h}{L} \right) = W_{rs} + W \frac{a_x}{g} \frac{h}{L}$$.

9. Tractive forces act on the ______
a) wheel patch
c) wheel contact patch
d) tire contact patch

Explanation: Tractive forces drive the vehicle. They act in the longitudinal direction during a straight-line motion in the tire contact patch.

10. Which among the following is most likely to be higher in a front-mounted engine pickup truck that is unloaded?
a) Static load on the rear axle on a level ground
b) Dynamic load on the front axle on level ground during low-speed acceleration
c) Dynamic load on the rear axle on level ground during low-speed acceleration
d) Static load on the front axle on a level ground

Explanation: Since the engine is front-mounted, the front axle static load would be large compared to the rear axle. Even during accelerating at slow-speeds, the load transfer to the rear will not be significant. Hence, static load on the front axle on level ground would most likely be more.

Sanfoundry Global Education & Learning Series – Vehicle Dynamics.

To practice all areas of Vehicle Dynamics, here is complete set of Multiple Choice Questions and Answers.

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