Chapter 2 Kinematics

Question 1

Scalar quantities

Answer 1

Remember scalar quantities only have a magnitude (size)

Distance: the total length between two points
-Speed: the total distance travelled per unit of time

Question 2

Vector quantities

Answer 2

• Remember vector quantities have both magnitude and direction
• Displacement: the distance of an object from a fixed point in a specified direction
• Velocity: the rate of change of displacement of an object
• Acceleration: the rate of change of velocity of an object

Question 3

On a displacement-time graph…

Answer 3

• slope equals velocity
• -the y-intercept equals the initial displacement
• a straight line represents a constant velocity
• -a curved line represents an acceleration
• a positive slope represents motion in the positive direction
• -a negative slope represents motion in the negative direction
• a zero slope (horizontal line) represents a state of rest
• -the area under the curve is meaningless

Question 4

On an acceleration-time graph…

Answer 4

• slope is meaningless
• the y-intercept equals the initial acceleration
• a zero slope (horizontal line) represents an object undergoing constant acceleration
• the area under the curve equals the change in velocity

Question 5

Area under a Velocity-Time Graph

Answer 5

• Velocity-time graphs show the speed and direction of an object in motion over a specific period of time
• -The area under a velocity-time graph is equal to the displacement of a moving object
• displacement = area under a velocity-time graph

Question 6

Gradient of a Displacement-Time Graph

Answer 6

• Displacement-time graphs show the changing position of an object in motion
• They also show whether an object is moving forwards (positive displacement) or backwards (negative displacement)
  
  • A negative gradient = a negative velocity (the object is moving backwards)
  • -The gradient (slope) of a displacement-time graph is equal to velocity
    
    • The greater the slope, the greater the velocity

Question 7

Gradient of a Velocity-Time Graph

Answer 7

• Acceleration is any change in the velocity of an object in a given time
• As velocity is a vector quantity, this means that if the speed of an object changes, or its direction changes, then it is accelerating
  
  • An object that slows down tends to be described as ‘decelerating’
  • The gradient of a velocity-time graph is equal to acceleration

Question 8

Deriving Kinematic Equations of Motion

Answer 8

• The kinematic equations of motion are a set of four equations which can describe any object moving with constant acceleration
• They relate the five variables:
  
  • s = displacement
  • u = initial velocity
  • v = final velocity
  • a = acceleration
  • t = time interval

Question 9

equations of motion

Answer 9

1. v = u + at
2. v²= u² + 2as
3. s = ut + 1/2at²
4. s= (u+v/2)xt

Question 10

Solving Problems with Kinematic Equations

Answer 10

1. Write out the variables that are given in the question, both known and unknown, and use the context of the question to deduce any quantities that aren’t explicitly given
   
   1. e.g. for vertical motion a = ± 9.81 m s–2, an object which starts or finishes at rest will have u = 0 or v = 0
2. Choose the equation which contains the quantities you have listed
   
   1. e.g. the equation that links s, u, a and t is s = ut + ½at2
3. Convert any units to SI units and then insert the quantities into the equation and rearrange algebraically to determine the answer

Question 11

Systematic error:

Answer 11

• Systematic Error
• *Faults in the apparatus or experimental method. Affects accuracy.**

Question 12

Random error

Answer 12

• Random Error
• *Unpredictable changes in an experiment causing one measurement to differ slightly from the next. Affects precision.**

Question 13

Projectile Motion

Answer 13

• The trajectory of an object undergoing projectile motion consists of a vertical component and a horizontal component
• These need to be evaluated separately
• Some key terms to know, and how to calculate them, are:
  
  • Time of flight: how long the projectile is in the air
  • Maximum height attained: the height at which the projectile is momentarily at rest
  • Range: the horizontal distance travelled by the projectile

Question 14

Remember:

Answer 14

• the only force acting on the projectile, after it has been released, is gravity
• There are three possible scenarios for projectile motion:
  
  • Vertical projection
  • Horizontal projection
  • Projection at an angle

Question 15

Km/h to m/s

Answer 15

Divide km/h value by 3.6