Mandatory Experiments: Mechanics

Question 1

ME 1: Acceleration due to Gravity: Between which points was the distance s measured? Describe how time t was measured?

Answer 1

Bottom of ball to top of trapdoor. Timer started when ball released and stopped when it hit and opened trapdoor.

Question 2

ME 1: Acceleration due to Gravity: Graph adjustments? Formula for experiment.

Answer 2

value for t squared and 2s
Plot 2s on y-axis and t squared on x-axis

s = ut + 1/2at^2

Question 3

ME 1: Acceleration due to Gravity: Accuracy: Why was a small dense ball used? Give two other ways of minimising air resistance/improving accuracy?

Answer 3

Less air resistance.

In vacuum
Distances relatively short

Question 4

Me 2: Acceleration is proportional to Force: Describe the steps involved in measuring the acceleration of the body.

Answer 4

1. Ticker tape timer puts 50 dots per second so time interval between consecutive dots is 0.02s
2. Velocity = distance between dots / 0.02 x number of spaces between distance measured.
3. Calculate initial and final velocities using ticker tape timer.
4. Calculate acceleration by subtracting initial from final velocity and then divide by 0.02 x number of spaces between middle of s1 (distance used when calculating initial) and middle of s2 (distance used when calculating final)

Question 5

Me 2: Acceleration is proportional to Force: What does the graph tell you about relationship? Why would it not go through origin?

Answer 5

F proportional to ma

1. Gravity
2. Friction

Question 6

Me 2: Acceleration is proportional to Force: 2 points of Accuracy.

Answer 6

Reduce friction by lubricating the trolley wheels and polishing table
Keep the table horizontal to minimise gravitational effects

Question 7

ME 3: Conservation of Momentum: State what measurements were taken? How was acceleration calculated?

Answer 7

Mass of both trolleys as m1 and m2.
Time interval = 0.02s multiplied by n gaps because ticker tape timer puts 50 dots per second on ticker tape.
Distance for n gaps

Time interval between consecutive dots is 0.02s as ticker tape timer puts 50 dots per second on ticker tape.
Calculate time interval which is 0.02 by number of spaces between n dots.
Use distance (for n dots) / time interval to calculate initial and final velocities.
Acceleration is equal to final - initial velocity divided by 0.02 by number of spaces in between the middle of the distances measured when calculating initial and final velocity.

Question 8

ME 3: Conservation of Momentum: How were measurement used to calculate velocities.

Answer 8

Distance / Time

Question 9

ME 3: Conservation of Momentum: What two external forces were minimised? How were they minimised? Formula?

Answer 9

Gravitational and frictional

Horizontal track reduces gravitational effects.
Lubricate the trolleys wheels and polish table.

m1u1 = {m1 + m2}v

Question 10

ME3: Conservation of Momentum: How did student A know that the body A was moving at a constant velocity? What adjustment was made to apparatus to ensure body A moves at constant velocity?

Answer 10

Dots on ticker tape timer equally spaced. Lubricate trolley wheels and adjust gradient of track.

Question 11

ME 3: Conservation of Momentum: 2 non friction or gravity accuracy points.

Answer 11

Avoid error of parallax when measuring distance between dots.
Avoid small values of velocities as measuring small values results in greater percentage errors.

Question 12

ME 4: Boyle’s Law: Procedure.

Answer 12

Read pressure from gauge and volume from scale.
Change pressure/volume and repeat measurements.

Question 13

ME 4: Boyle’s Law: Graph adjustments. How does graph verify Boyle’s law?

Answer 13

Reciprocal value of v on x-axis and pressure on y-axis

P proportional to inverse of volume

Question 14

ME 4: Boyle’s Law: Why might temperature have changed significantly during experiment? How can this be prevented?

Answer 14

Temperature is proportional to volume because of Charle’s Law so will vary depending on the volume.

Wait before making readings of temperature pressure to allow the gas to return to room temperature.

Question 15

ME 4: Boyle’s Law: Apart from keeping temperature constant what other accuracy procedures are there?

Answer 15

Using a gas-tight piston keeps mass of gas constant.
Avoid error of parallax when reading the volume of gas from the scale.
Avoid small values of volume as they result in greater percentage errors.

Question 16

ME 5: Investigate the laws of equilibrium for a set of coplanar forces: Explain how the centre of gravity was found. Explain how the weight of the metre stick was found.

Answer 16

Balance horizontally on a pivot

Suspend from newton balance

Question 17

ME 5: Investigate the laws of equilibrium for a set of coplanar forces: Explain how to ensure that the system is at equilibrium. Explain how the upward forces and downward forces are determined.

Answer 17

System not moving

Upward: newton balances
Downward: known weights

Question 18

ME 5: Investigate the laws of equilibrium for a set of coplanar forces: Why is the centre of gravity not at 50cm mark? Why does this experiment verify the laws of equilibrium?

Answer 18

Stick worn at one side
Stick has a hole in one side

Net vertical forces (0N)
Sum of moments around a point (0Nm)

Question 19

ME 6: Relationship between periodic time and length and calculation of g: Why did the student use a small angle? How did the student ensure the pendulum was suspended from a fixed point?

Answer 19

The formula is only valid for small angles where pieta is approximately equal to sin pieta.

The string was held between the two halves of a split cork.

Question 20

ME 6: Relationship between periodic time and length and calculation of g: Why did the student use a heavy bob and inextensible string? Between which points was the length of the string measured?

Answer 20

Heavy bob-To reduce air resistance and keep string taut.
Inextensible string-to keep the length constant.

Bottom of the cork to the middle of the bob.

Question 21

ME 6: Relationship between periodic time and length and calculation of g: What precautions were taken when allowing the pendulum to swing? (4) Why did the student measure 30 oscillations instead of one? What factors affect the accuracy of the periodic time measurement (4)?

Answer 21

No droughts, avoid spinning, one plane only, small angle.

Reduce error in the measurement. Improve accuracy.

Number of oscillations, precision of the timer, inextensible string, longer lengths lead to smaller % error.

Question 22

ME 6: Relationship between periodic time and length and calculation of g: Adjustments for graph? What does the graph show? How is g calculated? What is the formula?

Answer 22

Divide value of T by no. of oscillations before squaring.
Time squared on x-axis and l on y-axis.
T squared directly proportional to length

Slope x 4(pi squared) = g

As T squared = 4(pi squared) (length) / g