4.1 Video Motion Analysis using “Tracker”

Paste screen captures here with the following graphs for each of the 3 trials:

- Displacement – time graph
- Velocity – time graph
- Acceleration – time graph

4.2 Data Analysis

- Which wheels are you drive wheels? (front or back)

The rear wheels are the driving wheels of the car.

- What is the circumference of your drive wheels?

37.7cm (3 s.f.)

- How far will your car travel in one rotation of the drive wheels?

Since the circumference of the drive wheels is 37.7cm, one full rotation of the wheel should allow the car to travel a distance of approximately 37.7cm.

- How many rotations (on average ) were there in each run?

On average, there was approximately 24 rotations per run.

- How much string is used in one rotation of the drive wheels? Show how you calculated this.

Amount of string used in 1 rotation

= circumference of axle

= 2 x π x 0.5cm

= 3.14cm (3.sf.)

= circumference of axle

= 2 x π x 0.5cm

= 3.14cm (3.sf.)

- The release of the lever is the power stroke. What is the length of your vehicles power stroke? (Length of string released)

Power stroke: 40cm

- Calculate how far your vehicle will travel during the power stroke. Show your calculations!!

Number of round of coils x Circumference of wheel

= Distance car will travel during power stroke

= Distance car will travel during power stroke

= 12 x 37.7cm

= 452.4cm = 4.52m (3sf)

- Compare the answer to #7 to the distance your measured during your car’s power stroke. Discuss possible reasons for different values.

We did not take into account the presence of friction and air resistance in our calculations.

- Calculate the average velocity for your car during the period after the spring fully releases.

Average distance the car travels according to the 3 trials = 9m

Average velocity after the spring fully releases

= (v-u)/t

= (9m-4.52m)/3s

= 1.49m/s (3 s.f.)

- What force causes your car to stop?

The car starts to slow down and stopped because of air resistance and the frictional force acting on the wheels as the car travels.

- The work done by a force is calculated by multiplying the force times the distance over which it acts. The work done on an object is equal to the change in its kinetic energy. Can you find a way to calculate the force of friction? Use equations and explain your steps. HINT: Be careful, you have calculated average velocity. How can you find the total amount of kinetic energy (immediately after spring release) if we assume the acceleration during coasting was constant?

Work done = Force * Distance (travelled after string releases)

Work done = Kinetic Energy

F = mass of car * acceleration

A= Gradient of Velocity-Time Graph

F = 0.325kg * 1.49m/s^2

F = 0.484N (3 s.f.)

Newton’s 3rd Law

Reaction Force = Opposite Force

Frictional Force = 0.484N

Work done = 0.484N * 5m

= 2.42J

Work done = Kinetic Energy

Kinetic Energy = 2.42J

- Various experiments have been done to measure the potential energy available from the spring. One estimate is 0.65 Joules. Using your estimates of the maximum kinetic energy of your car and the work done by friction, discuss whether or not this is a reasonable value. Can you account for any differences in the forms of energy? You must justify all of your arguments.

Energy cannot be destroyed or created, it can only be converted to different forms of energy. Based on the previous question, we could calculate the Kinetic Energy, which was 2.42J. The energy source of the mousetrap car comes from the Elastic Potential Energy which is stored in the spring of the mouse trap. When the mouse trap car moves, the elastic potential energy is converted to other forms of energy such as kinetic energy, heat energy and sound energy. That means Elastic Potential Energy = Kinetic Energy + Heat Energy + Sound Energy. Since the Kinetic Energy is 2.42J. Therefore our group disagrees with the estimation and the estimation of the Elastic Potential Energy is not a reasonable value.

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