# Need help with calculus for a car! (admission test question)

1. Feb 27, 2010

### much12

In this question you will use a simple model to estimate how the energy used
by a car depends on its design and how it is driven. Begin by neglecting air
and ground resistance, and assume that the car travels at constant velocity
between regular equally spaced stops.

(a) A stationary car of mass m is rapidly accelerated to a velocity v, driven
for a distance s, and is rapidly brought to a halt by its brakes. Calculate
the energy dispersed by the brakes.

(b) Assuming the car restarts immediately, calculate the time between
subsequent stops and hence the average power dissipated.

(c) Hence or otherwise calculate the energy used in travelling a total distance
d.

(d) Taking m = 1000 kg, v = 10ms−1 and s = 100m calculate the energy
used in travelling 1 km. What would be the effect of doubling the speed
to 20ms−1?

I need help with this Question. It seems to be easy but I think I've got an error in my mind.^^

2. Feb 27, 2010

### Mindscrape

What are you thinking of so far, what would the work energy theorem say? How do you think power relates to work?

Try it out some and let us know exactly where you're stuck.

3. Feb 28, 2010

### much12

I thought that a system that is not accelerated has no resultant force (since you may neglect air and groung resistance). So, all the energy will be kinetic energy. E = (mv^2)/2.
Then I got stuck in the second Question.
So, I need the equation or a hint to solve question (b) and (c).