# Year 11 Physics Assignment

1. Jul 7, 2005

### Physics_Student101

Hello everyone,

Im new to this forum so im not entirely sure how it works,
I have a physics assignment in which i must analyse kinematics, impulse and momentum, friction, energy and circular motion, im currently working on a car design and i was wondering if anyone could tell me the formulae i need to analyse the force on an impact on a car travelling at a certain speed lets say 60km/h colliding with a tree.

2. Jul 8, 2005

### OlderDan

You can estimate the force by assuming a constant deceleration and constant force during the time of impact. Under this assumption, you can find the acceleration from the change in velocity and the distance the car moves while it is stopping, which would be the amount by which the car crumples on impact (a half meter or so perhaps). The equation that relates these quantities is

$$v_{final}^2 - v_{initial}^2 = 2as$$

where s is the stopping distance and a is the acceleration (negative for stopping). Once you have the acceleration, the force acting on the car is found from Newton's second law

$$F = ma$$

Obviously it takes more force to stop a more massive car.

3. Jul 8, 2005

### NewScientist

Year 11 - So it's coursework, that brief is fairly large, when I visited a school recently their question was quite fixed and not open ended, perhaps you could tell us your brief more succintly?

-NewScientist