# Simple question of acceleration

1. Feb 21, 2010

### RoryOBigtool

1. The problem statement, all variables and given/known data
An unloaded lorry of mass M kg accelerates from rest and reaches a velocity of 30mph in 10 seconds. It then travels at constant velocity for half a minute before the driver applies the brakes and brings the vehicle to rest over a distance of D m.
The lorry is then loaded with 800 kg of building materials that need to be transported over a total distance of 0.6 km. After loading, the lorry accelerates over a distance of 80m to attain a velocity of 30mph again. The vehicle subsequently maintains constant velocity before decelerating to rest at a rate of R m/s2.

M=2300KG D = 70m R = 1.5m/s^2

2. Relevant equations
The questions exactly

i) the force required to accelerate the vehicle, and the retarding force necessary to bring it to rest;
ii) the total time and the total distance travelled during this period.

Find for the loaded lorry :

i) the force required to accelerate the vehicle and the retarding force necessary to bring it
to rest;

ii) the total time taken during this period and the distance travelled at constant velocity.

c) Calculate the % change in the momentum of the lorry from loaded to unloaded, whilst travelling at the specified constant velocities.

d) Draw the ‘velocity-time’ graph of the motion of the lorry in its unloaded and loaded states, indicating clearly salient points and values.

3. The attempt at a solution
I tried using V^2 = U^2 +2as , V=S/t and general thinking but im 100% sure that im incorect. i got answers like 0.65 m/s^2 which seemed possible but it is half the acceleration than when the lorry was unloaded, i think half is too little if only 800KG was added. i also got stupid answers like 15.67 m/s^2

can some one help me

Last edited: Feb 21, 2010
2. Feb 21, 2010

### ideasrule

Read your own post again and you'll see why I can't understand it at all. What information is provided about the unloaded lorry? What's the actual question? Why does the 0.6 km matter?

3. Feb 21, 2010

### PhanthomJay

I believe you left out some info regarding the unloaded lorry, like its acceleration, speed, etc. And you left out the question as well. Please re-write this problem in its entirety.

4. Feb 21, 2010

### RoryOBigtool

hey i edited the original message. i think i have got the full way to B) correctly. I need B to continue though, so you can see my de lima. I usually know what im talking about when it comes to physics but this has really stumped me!! any help is a positive result :)

Also does anyone know the value of e in the equation of electric field strength ( E = 1 / 4(pie) eo er x Q1Q2/r^2 )?

Last edited: Feb 21, 2010