Ryan ThomasA.P. Physics10/8/07

Mass of the Car Write Up

Purpose: To determine the mass in kilograms and the rolling friction force of a car.

Equipment: 1997 Honda Civic 2 Bathroom Scales Tape Measure Stop Watch Marker Cones

Assumptions:The main assumption made in the calculations is that air resistance does not act on

the car during the experiment; this serves to simplify calculations, and will not significantly alter results, as the force of air resistance here is minimal. Other assumptions are that the figures collected are accurate and that they are precise; also, the force on the car is assumed to be constant.

Calculations: Known Information: The car begins moving from an inert state as 40 lbs of force are exerted upon it. With a constant 100 lbs of force upon it, the car moved 20.5 m in 30 sec.The coefficient of the static friction of the tires against the concrete is 1.0.

Problem: Find the mass of the car and the force of rolling friction on the car.

Step 1 – Calculate the car’s mass

Since the static friction working on the car is overcome when a force of 40 lbs is exerted upon it,

μFN = 40 lbs

And by plugging in the coefficient of static friction, we get

FN = 400 lbs = (400 lbs * 4.45 N / lb) = 1780 N

Now, FN in this case equaling mg, we can see that

mg = 1780 N; m = 1780 N / 9.8 m/s2 = 181.6 kg

Step 2 – Calculate the rolling friction force of the car

First, to find the acceleration of the car:o 100 lbs * 4.45 N = 445 N of force, assumed constanto 445 kg * m/s2 =