Mechanics

Question 1

What is the difference between uniform and non- uniform motion?

Answer 1

Uniform motion – acceleration is constant (including an acceleration of 0m/s2)

Non-uniform motion – acceleration is not constant

Question 2

What do the slopes and areas under the graphs of the graphs below tell you:

Displacement-time
Velocity-time
Acceleration-time

Answer 2

Displacement-time graph:

Gradient = velocity
Area = nothing

Velocity-time graph:

Gradient = acceleration
Area = displacement

Acceleration-time graph:

Gradient = nothing
Area = change in velocity

Question 3

Define distance.

Answer 3

How far something travels.

Question 4

Define displacement.

Answer 4

How far an object travels from its starting point in a given direction.

Question 5

Define speed.

Answer 5

The distance travelled by the object in a given time.

Question 6

Define average speed.

Answer 6

the total distance travelled by the object divided by the total time.

Question 7

Define instantaneous speed.

Answer 7

The speed of an object at a given time.

Question 8

Define velocity.

Answer 8

The rate of change of displacement.

Question 9

Define average velocity.

Answer 9

The total displacement divided by the total time.

Question 10

Define instantaneous velocity.

Answer 10

The velocity at a given time.

Question 11

How could you find the instantaneous velocity and average velocity from a displacement-time graph?

Answer 11

Instantaneous velocity – draw a tangent at a given point, and determine the gradient (using as big a triangle as possible)

Average velocity – total distance/displacement divided by time

Question 12

Describe how the bouncing ball graphs would be similar/different for a softer/less inflated ball?

Answer 12

The

The time taken for the balls to hit the ground will be the same

The maximum displacement of each bounce will decrease as kinetic energy is lost due to friction between the ground and the ball.

The maximum velocity would decrease due to the reduction in kinetic energy.

The gradient of the velocity-time graph will be the same as gravity (the force only acting on the ball) is always 9.81ms^2.

The gradient of the velocity-time graph where the ball makes contact with the ground will be less steep as the time taken for the ball to change directions is longer.

Question 13

What is the difference between scalar and vector quantities?

Answer 13

Scalar quantities only have magnitude

Vector quantities have magnitude and direction

Question 14

List common scalars.

Answer 14

Temperature, energy, power, work done, current.

Question 15

List common vectors.

Answer 15

Force, velocity, acceleration, displacement, moment/torque.

Question 16

For a projectile moving under gravity, describe the horizontal motion.

Answer 16

Constant

Question 17

For a projectile moving under gravity, describe the vertical motion.

Answer 17

-9.81ms^2 as the only force acting is gravity.

Question 18

Define Newton’s first law.

Answer 18

The velocity of an object will not change/remain at rest/move in a straight line with constant speed, unless there is a resultant force acting on it.

Question 19

Define Newton’s second law.

Answer 19

The acceleration of a body is proportional to the resultant force.

F = ma

Question 20

Define Newton’s third law.

Answer 20

If an object A exerts a force on object B, then object B must exert a force of equal magnitude and opposite direction back on object A.

Question 21

What properties must be true for Newton’s third law pairs of forces?

Answer 21

The pair of forces must be the same type of force acting in opposite directions and in the same plane.

Question 22

What does a free-body force diagram show?

Answer 22

A free-body force diagram shows all the forces acting on a single body.

It should not include forces exerted on the environment around the body, or the forces acting on a second object.

Question 23

What does it mean to resolve forces/vectors?

Answer 23

Resolving a force is splitting a single force into its components.

Question 24

What does it mean to add forces/vectors?

Answer 24

If two or more forces acting on an object, the resultant force can be found by adding the components together.

Question 25

Define Newton’s second law in terms of an equation. What must you be careful of?

Answer 25

F=ma F is the resultant force; this may need to be found first, or it may not be the force you have been asked for.

Question 26

What are the two main types of friction?

Answer 26

Friction between solid surfaces Friction in a fluid (aka drag). Air resistance is an example of fluid resistance. Fluid resistance is affected by viscosity.

Question 27

What do frictional forces always cause?

Answer 27

A force that is opposite to the direction of motion. Kinetic energy is converted to heat and sound.

Question 28

Describe what causes an object to reach terminal velocity.

Answer 28

Initially, there will be a resultant force. This resultant force causes the object to accelerate. As the velocity increases, the drag increases. This reduces the resultant force, therefore reduces the acceleration Eventually, the fluid resistance will be equal to the driving force or weight. There is no resultant force, therefore no acceleration. The object is moving at a constant speed, called terminal velocity).

Question 29

What factors affect the terminal velocity of a car?

Answer 29

Size of the driving force. Size of the frictional force.

Question 30

What equation is used to calculate the weight of something?

Answer 30

W = mg

Question 31

Define momentum.

Answer 31

Momentum is the product of the mass of an object and its velocity.

Question 32

Define the principle of conservation of linear momentum.

Answer 32

The total momentum before a collision or explosion is equal to the total momentum after providing no external forces act.

Question 33

Define Newton’s laws in terms of momentum.

Answer 33

Newton’s First Law: The momentum of a body remains constant, unless there is a resultant force. Newton’s Second Law: If the is a resultant force, the rate of change of momentum is directly proportional to the resultant force, and in the same direction. Newton's Third Law: If two objects collide, they exert an equal and opposite force on each for the same time. So momentum is conserved.

Question 34

What is Newton’s second law, in terms of moment as a formula?

Answer 34

F = mv / t Ft = mv

Question 35

Define a moment.

Answer 35

Force multiplied by the perpendicular distance from the line of action of the force and the axis of rotation.

Question 36

Define centre of gravity.

Answer 36

The single point of an object that you can consider its whole weight to act through.

Question 37

State the conditions needed for something to be in equilibrium.

Answer 37

Resultant force in any direction is zero. Sum of the moments about any point is zero. If there are 3 forces acting, you should be able to close a triangle

Question 38

Define work done.

Answer 38

Work is done when a force is used to move something a distance in the same direction as the force is acting. It is usually the same as energy transferred. Work is usually done against another force (e.g. work done against gravity, work done against friction). W = Fs

Question 39

What is the equation for kinetic energy?

Answer 39

(1/2)mv^2

Question 40

What is the equation for gravitational potential energy?

Answer 40

mgh

Question 41

What is the equation for power?

Answer 41

P = W / t

Question 42

What is the equation for efficiency?

Answer 42

Useful (energy/power out / total energy input) x 100

Question 43

What is power?

Answer 43

The rate of doing work/how much energy is transferred per second.

Question 44

State the principle of conversation of energy.

Answer 44

Energy cannot be created or destroyed. Energy can be transferred from one form to another but the total amount of energy in a closed system will not change.

Question 45

Why does a bouncing object never return to its original height

Answer 45

Work is done against friction of the ball and the ground or air resistance. Some energy is converted to thermal energy therefore less energy is available as gravitational potential energy.

Question 46

Why will a rollercoaster never return to its original height?

Answer 46

Work is done against friction of the wheels and the track or air resistance. Some energy is converted to thermal energy therefore less energy is available as gravitational potential energy.

Question 47

Define a newton.

Answer 47

1 Newton is force needed to give a mass of 1kg an acceleration of 1 ms^2

Question 48

Define a joule.

Answer 48

1 Joule is the work done by a force of 1 newton when its point of application moves 1 metre in the direction of action of the force

Question 49

Define a watt.

Answer 49

1 Watt is when 1 joule of energy is transferred per second

Question 50

Describe the "CPAC 1: Determine the acceleration of a freely-falling object." experiment.

Answer 50

1) Clamp an electromagnet to a stand with a trapdoor a set distance (measured with a metre ruler) below the electromagnet. 2) The electromagnet and trapdoor are attached to a timer where when the switch for the electromagnet is turned off, the timer starts and is stopped when the object passes through trap doors. 3) Turn the switch on and attach a small, heavy metal ball bearing to the electromagnet (to assume air resistance is small and therefore negligible). 4) Turn the switch off to release the ball and start the timer and when the ball passes through the trapdoor the timer will stop. Record the time. 5) Repeat this experiment 3 times and take an average of the three times. 6) Repeat this experiment for different distances. 7) Use these results to plot a graph of height over (time taken to fall)^2. This is done by rearranging the suvat equation (s = ut + (1/2)at^2) to get "a": (1/2)a = s / t^2. 8) The gradient of the line will determine the acceleration halved so multiply the gradient by 2 to get the acceleration. 9) Calculate a percentage difference from your answer compared to gravity (the actual deceleration) to evaluate the accuracy of your answer.