Vehicle Of Mass 2000 Kg Accelerates Up An Incline Of 1 In 1

A Vehicle Of Mass 2000kg Accelerates Up An Incline Of 1 In 12 Sine I

A vehicle of mass 2000 kg accelerates up an incline of 1 in 12 (sine), increasing its speed from 15 km/h to 55 km/h while traveling through a distance of 150 meters up the slope. The four wheels each have a mass of 20 kg, a diameter of 0.6 meters, and a radius of gyration of 250 mm. The total resistance to motion due to rolling friction, air resistance, and bearing friction amounts to 0.5 kN. Calculate the tractive effort between the driving wheels and the road surface, the work done during the period of acceleration, and the average power developed.

Paper For Above instruction

Introduction

Understanding the dynamics of a vehicle accelerating along an incline involves analyzing forces acting on the vehicle, including resistive forces, gravitational components, and the effort exerted by the engine through the wheels. This problem encompasses calculating the traction (tractive effort), work done during acceleration, and the power developed by the vehicle's engine, considering various physical parameters such as mass, resistance, and kinematics.

Analysis of the problem

The vehicle's journey involves accelerating from an initial speed of 15 km/h to a final speed of 55 km/h over a distance of 150 meters up a slope inclined at a ratio of 1 in 12. The key parameters provided include vehicle and wheel masses, wheel dimensions, resistance to motion, and the inclination ratio, which can be used to derive the inclination angle.

Conversion of units and initial calculations

Speed conversion:

- Initial speed \( u = 15 \text{ km/h} = \frac{15 \times 1000}{3600} \text{ m/s} \approx 4.17 \text{ m/s} \)

- Final speed \( v = 55 \text{ km/h} = \frac{55 \times 1000}{3600} \text{ m/s} \approx 15.28 \text{ m/s} \)

Incline angle:

Given a ratio of 1 in 12, the incline angle \(\theta\) can be obtained as:

\[

\sin \theta = \frac{1}{12} \approx 0.0833

\]

Thus, the angle \(\theta \approx \arcsin(0.0833) \approx 4.77^\circ\).

Average acceleration:

Using the kinematic relation:

\[

v^2 = u^2 + 2 a s

\]

\[

a = \frac{v^2 - u^2}{2 s} = \frac{(15.28)^2 - (4.17)^2}{2 \times 150} \approx \frac{233.4 - 17.4}{300} = \frac{216}{300} \approx 0.72 \text{ m/s}^2

\]

Time taken during the acceleration:

Using \( v = u + at \):

\[

t = \frac{v - u}{a} = \frac{15.28 - 4.17}{0.72} \approx \frac{11.11}{0.72} \approx 15.43 \text{ s}

\]

Dynamic calculations

1. Calculation of resistance forces:

Total resistance \( R = 0.5 \text{ kN} = 500 \text{ N} \).

2. Calculation of gravitational component along the incline:

\[

F_{gravity} = m g \sin \theta

\]

where \( g = 9.81 \text{ m/s}^2 \), \( m = 2000 \text{ kg} \):

\[

F_{gravity} = 2000 \times 9.81 \times 0.0833 \approx 2000 \times 0.817 \approx 1634 \text{ N}

\]

3. Total resistive force:

\[

F_{resist} = R + F_{gravity} = 500 + 1634 = 2134 \text{ N}

\]

4. Calculation of the tractive effort \(F_t\):

The net force required for acceleration is:

\[

F_{net} = m a = 2000 \times 0.72 = 1440 \text{ N}

\]

The total tractive effort must overcome resistive forces and provide acceleration:

\[

F_{tractive} = F_{resist} + F_{net} = 2134 + 1440 = 3574 \text{ N}

\]

This effort is exerted at the wheel-road interface.

5. Torque and rotational inertia considerations for the wheels:

Wheel Moment of Inertia:

The moment of inertia of each wheel is:

\[

I = \text{Gyration} \times m_{wheel} \times r^2

\]

Given:

- Gyration radius \( k = 0.25 \text{ m} \)

- Wheel mass \( m_{w} = 20 \text{ kg} \)

- Wheel radius \( r = 0.3 \text{ m} \)

\[

I = m_{w} k^2 = 20 \times (0.25)^2 = 20 \times 0.0625 = 1.25 \text{ kg.m}^2

\]

Total rotational inertia for four wheels:

\[

I_{total} = 4 \times 1.25 = 5 \text{ kg.m}^2

\]

Angular acceleration of the wheels:

\[

\alpha = \frac{a}{r} = \frac{0.72}{0.3} \approx 2.4 \text{ rad/s}^2

\]

Torque required to accelerate wheels:

\[

T_{wheels} = I_{total} \times \alpha = 5 \times 2.4 = 12 \text{ Nm}

\]

Total tractive effort at the wheels:

Wheel torque relates to force as \( F_{wheel} = T / r \):

\[

F_{wheel} = \frac{12}{0.3} = 40 \text{ N}

\]

Since the torque accounts for rotational effects, the overall effort required at the contact patch, considering the resistances and drive, remains approximately 3574 N, with the rotational inertia effects being relatively small but accounted for in torque calculations.

Work done during acceleration

The work done is the change in the kinetic energy plus work overcoming resistances:

\[

W_{total} = \Delta KE + W_{resistance}

\]

Change in kinetic energy:

\[

\Delta KE = \frac{1}{2} m v^2 - \frac{1}{2} m u^2

\]

\[

= 0.5 \times 2000 \times (15.28^2 - 4.17^2) \approx 1000 \times (233.4 - 17.4) = 1000 \times 216 = 216,000 \text{ J}

\]

Work against resistances:

\[

W_{resistance} = R \times s = 500 \times 150 = 75,000 \text{ J}

\]

Total work done:

\[

W_{total} = 216,000 + 75,000 = 291,000 \text{ J}

\]

Note: This calculation assumes all work goes into kinetic energy and overcoming resistances; actual work includes rotational and other losses, but they are minimal here.

Average power developed

Power is work over time:

\[

P_{avg} = \frac{W_{total}}{t} = \frac{291,000}{15.43} \approx 18,840 \text{ W} \approx 18.84 \text{kW}

\]

Alternatively, calculating power at the final velocity:

\[

P_{instantaneous} = \text{tractive effort} \times \text{vehicle speed} + \text{resistive power}

\]

\[

= 3574 \times 15.28 + 500 \times 15.28 \approx 54,544 + 7,640 = 62,184 \text{ W}

\]

Using average values over acceleration yields the approximate mean power as about 18.84 kW.

Conclusion

The vehicle requires a tractive effort of approximately 3574 N to overcome resistive forces and accelerate up the incline. The total work done during this acceleration is around 291 kJ, and the average power developed by the engine over the acceleration period is approximately 18.84 kW. These calculations integrate the effects of gravitational components, resistance, rotational inertia, and kinematic parameters, illustrating the complex interplay of forces involved in vehicle motion on an incline.

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