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

View Answer

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 W_{fs} = 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

View Answer

Explanation: W

_{fs}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 W

_{rs}= 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

View Answer

Explanation: Static load on the front axle on level ground is given by W

_{fs}= W\(\frac{c}{L}\). Static load on the rear axle on level ground is given by W

_{rs}= 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 W

_{fs}=W

_{rs}. 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

View Answer

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) W_{fs}-W\(\frac{h}{L}\)θ

b) W_{rs}+W\(\frac{h}{L}\)θ

c) W_{fs}+W\(\frac{h}{L}\)θ

d) W_{rs}-W\(\frac{h}{L}\)θ

View Answer

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 W

_{rs}+W\(\frac{h}{L}\)θ. And, the load on the front axle becomes W

_{fs}-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

View Answer

Explanation: Static load on the front axle is given by W

_{fs}=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/s

^{2}. The weight of the car is W=mg=19620 N. Therefore, the static load on the front axle becomes W

_{fs}=W\(\frac{c}{L}\)=19620⋅\(\frac{1}{2}\)=9810 N.

7. At low-speed dynamic axle load always remains constant.

a) True

b) False

View Answer

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

View Answer

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

b) road patch

c) wheel contact patch

d) tire contact patch

View Answer

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

View Answer

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.**

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