DD49 Posted June 5, 2006 Report Share Posted June 5, 2006 Hello all. First time visiting the forums. Looks quite something. Ive got a little, well quite big for me question im struggling on which led me to these forums. Was wondering if i would find help here. It goes like this. A car of mass 750kg accelerated uniformly whilst ascending an incline of gradient 1 in 20. The speed increases from 10kmh (power of minus 1) to 80kmh(power of minus 1) during a time of 10 seconds and frictional resistance can be neglected. Now what ive got to determine from that is this: 1. The tractive effort at the driving wheels and the work done during the acceleration period using the equations of motion and Newtons 2nd law of motion 2. The work done and the tractive effort during the acceleration period using an appropriate energy method. Ive given it a go and got a whole load of working out here but struggle to piece it together for whats needed. If i had a scanner i could show you what i mean. If anyone could give me an insight into this i would be ever grateful :( Quote Link to comment Share on other sites More sharing options...

Tim_Lou Posted June 5, 2006 Report Share Posted June 5, 2006 1. i dont quite get the question, what do you mean by "tractive effort"? 2. work done by what? gravity? if so, the work would simply be the change in kinetic energy (assuming no friction, no air resistance) well, i suppose you want to include the rotation of the wheel. this can be done by comparing the ratio of the actual acceleration to the acceleration without any rotational affect. if you could specific things on the question i might be able to help you out more. Quote Link to comment Share on other sites More sharing options...

CraigD Posted June 6, 2006 Report Share Posted June 6, 2006 A car of mass 750kg accelerated uniformly whilst ascending an incline of gradient 1 in 20. The speed increases from 10kmh (power of minus 1) to 80kmh(power of minus 1) during a time of 10 seconds and frictional resistance can be neglected.This is a fairly uncomplicated problem in mechanics, with a couple of simplifying assumptionsThe acceleration of the car is constant (otherwise, the distance calculation required for question 2 below becomes complicated)The car’s wheels are effectively massless (so we don’t need to consider the amount of energy stored in them)1. The tractive effort at the driving wheels and the work done during the acceleration period using the equations of motion and Newtons 2nd law of motionThis force has 2 components:[math]F_{total}=F_{gravity}+F_{acceleration}[/math][math]F_{gravity}=g * Sine \Theta * Mass [/math][math]F_{acceleration}= A * Mass [/math][math]A=\frac{(V_{final} - V_{initial})}{time}[/math][math]Sine \Theta[/math], [math]Mass[/math], [math]V_{initial}[/math], [math]V_{final}[/math], and [math]time[/math] are all given in the problem, while [math]g[/math] is a constant, the acceleration of gravity for the earth’s surface, about [math]9.81 m/s^2[/math]. We have what we need to calculate [math]F_{total}[/math]2. The work done and the tractive effort during the acceleration period using an appropriate energy method.Here, all that’s needed is the definition of work:[math]W=F_{total}*D[/math]Having assumed constant acceleration, we can use a simple formula for[math]D=\frac{(V_{initial} + V_{final})}{2}[/math] The tradition here at hypography is for the question poster to calculate and post their calculations and results, and folk offering guidance to let them know if they’ve made any mistakes. Happy calculating! :) Quote Link to comment Share on other sites More sharing options...

Qfwfq Posted June 7, 2006 Report Share Posted June 7, 2006 Is it homework? If so, you can ask help in "Science Projects and Homework". ;) Quote Link to comment Share on other sites More sharing options...

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