1. Motion Forces & Energy (INCOMPLETED)

Question 1

Describe the use of rulers to find a length

Answer 1

Rulers are used to measure lengths:
- Object must be straight, laid alongside the ruler (in contact)
- Consider the ends of the object (start from 0)
- Look at the markings on the ruler (best to use a ruler with mm)
- Look at the other end of the object and read the scale (eyes should be at the same level of the marking to avoid parallax error)

Question 2

Describe the method of using measuring cylinders to find a volume

Answer 2

Measuring cylinder can be used to measure volume:
- Choose an appropriate measuring cylinder
- Look at the scale horizontally and read the level at the bottom of the meniscus (upper surface of the liquid)

Question 3

Describe how you can use the displacement method for irregular shaped objects

Answer 3

Irregularly shaped object, we use displacement:
- Select a measuring cylinder three or four times larger than the object
- Fill it with water enough to cover the object
- Immerse the object in water
- Subtract the measurement after placing the object and the measurement before

Question 4

Describe how to measure a variety of time intervals using clocks and digital timers

Answer 4

Using clocks;
- Analogue: to the nearest second
- Digital: direct reading of the time in numerals

Using digital timers;
- Basic: (normal stopwatches)
- Advanced: (stopwatches with laps)

→ Stop-clocks and stopwatches can be used to measure time intervals

Question 5

How to determine an average value for a small distance and for a short interval of time by measuring
multiples?

Answer 5

For a small distance, example the thickness of one piece of paper;
- Calculate the average thickness of one sheet = thickness of stack ÷ number of sheets

For a short interval of time, example the period of oscillation of a pendulum;
- Calculate the average time per oscillation = time taken for 10 swings ÷ number of swings

Question 6

Whats the difference between Scalar and Vector quantity?

Answer 6

Scalar quantity has magnitude (size) only whereas vector quantity has magnitude and direction

Question 7

List the examples of Scalar and Vector quantity

Answer 7

• Scalars: distance, speed, time, mass, energy and temperature
• Vectors: force, weight, velocity, acceleration, momentum, electric field strength and gravitational field strength

Question 8

How can Vectors be combined?

Answer 8

1. The Triangle Method
   - Used when the arrow of vector A touches the tail of vector B (triangle)
   - Resultant vector (C) is the hypotenuse of the triangle
2. The Parallelogram Method
   - Used when vectors A and B form a right angle and its tails connect (rectangle)
   - Resultant vector (C) is the diagonal line of the rectangle

Question 9

How to determine, by calculation, the resultant of two vectors at right angles?

Answer 9

1. Using trigonometry: When the magnitude of one vector and the angle is known
   SOH: sin = opposite/hypotenuse
   CAH: cos = adjacent/hypotenuse
   TOA: tan = opposite/adjacent
2. Using pythagoras’ theorem: When the magnitudes of two of three vectors are known
   c² = a² + b²

Question 10

Define speed

Answer 10

Speed (m/s): Distance travelled (m) per unit time (s)

Question 11

Define velocity

Answer 11

Speed in a given direction

Question 12

What is the formula for the average speed?

Answer 12

Average Speed = Total Distance Travelled ÷ Total Time Taken

Question 13

Define acceleration

Answer 13

Change in velocity per unit time

Question 13

What is the formula for Acceleratiom?

Answer 13

A = (v-u)/t

Question 14

How to calculate speed from the gradient of a straight line section of a distance–time graph

Answer 14

Gradient = speed = change of y ÷ change of x = distance travelled ÷ time taken

Question 15

How to calculate acceleration from the gradient of a speed–time graph

Answer 15

Gradient = acceleration = (v-u)/t = change in speed ÷ time

Question 16

How to calculate the area under a speed–time graph to determine the distance travelled

Answer 16

Area under a speed-time graph represents the distance
- Distance = Area of the shape
- Can be calculated by finding the area of each shape and then adding them together

Question 17

What type of acceleration is deceleration?

Answer 17

Deceleration is a negative acceleration therefore use -ve when calculating

Question 18

State the formula for weight

Answer 18

W (N) = mass (kg) x gravitational field strength (9.8N/kg)

Question 18

What is the acceleration of free fall g for an object near to the surface of the Earth?

Answer 18

Acceleration of free fall g (gravitational field strength) for an object near to the surface of the Earth is approximately constant and is approximately 9.8m/s² due to gravity

Question 19

Describe the motion of objects falling in a uniform gravitational field with air/liquid resistance (include reference to terminal velocity)

Answer 19

• Objects falling in liquid will face an exerted frictional force which opposes the motion
• Objects falling through air experiences air resistance and the force of weight
• Air resistance increases as the speed of the object increases
• When air resistance and weight reach equilibrium, the object falls at a constant speed (terminal velocity)

Question 20

Describe the motion of objects falling in a uniform gravitational field without air/liquid resistance (include reference to terminal velocity)

Answer 20

• In a vacuum, there’s no particles to exert frictional force therefore no air/liquid resistance except for the force of weight
• So for objects falling in a vacuum, a = g (acceleration of free fall)
• Objects will never reach a terminal velocity