# Dynamics Flashcards

1
Q

What does this velocity-time graph show?

A

Constant velocity

2
Q

How can you increases friction?

A
• Increase the area of the rubbing surfaces
• Make the rubbing surfaces rougher
• Push the rubbing surfaces togerther more
• Increase the speed that the surafces are rubbed together
3
Q

Describe how a cyclist can streamline themself

A
• Crouch over the handlebars
• Wear tight lycra clothing
• Specially shaped helmet
4
Q

What is a balanced force?

A

Equal forces acting in opposite directions

5
Q

Newtons 1st Law is about balanced forces, what two things can happen if a balanced force acts on an object?

A
• Remains stationary
• Travels at a constant speed in a straight line
6
Q

What is acceleration?

A

Acceleration is the rate of change of velocity or the change in velocity per second.

7
Q

What is the difference between distance and displacement?

A

Distance is the length of the path you actually take and it is a scalar, displacement is the straight line distance between where you started and finished including a direction as it is a vector.

8
Q

Which line on the graph represents the largest acceleration?

A

Blue Line - it has the steepest gradient

9
Q

What is the difference between mass and weight?

A

Mass is a measure of the partcles that make an object up. Weight is a force caused by the gravitational field strength of a planet.

10
Q

What is speed?

A

Distance travelled per second.

11
Q

Name three vector quantities

A
• Displacement
• Velocity
• Acceleration
• Force
• Momentum
• Weight
12
Q

An astronaut has a mass of 50kg. What will happen to the astronauts mass on the Moon?

A

It stays at 50kg. Mass does not change.

13
Q

An astronaut has a mass of 50kg. What will happen to the astronauts weight on the Moon?

A

The weight will decrease as there is a lower gravitaional field strength on the Moon.

14
Q

What is meant by gravitational field strength?

A

Force per unit mass

15
Q

What is meant by an acceleration of 15ms-2 ?

A

The velocity increases by 15ms-1 every second.

16
Q

Explain the difference between average and instantaneous speed.

A

Average speed is over a long period of time, Instantaneous speed is the speed over a very short period of time.

17
Q

If an object is projected horizontally from a cliff, how can the height of the cliff be calculated?

A
• Sketch a vertical velocity-time graph
• Due to gravitational field strength the velocity will increase vertically by 9.8ms-1.
• Calculate the area under the velocity-time this is equal to the verical height of the cliff.
18
Q

What will an unbalanced force cause?

A

Acceleration

19
Q

Explain how to measure acceleration using the equipment shown below and a stop watch.

A
• When the cardboard passes through the first light gate the timer attached to it records this time.
• Measure the length of the card with a ruler.
• The initial velocity, u = length of card / time on timer
• As the car rolls down the ramp, start the stop watch when it reaches the first light gate and when it reaches the second light gate stop the stop watch.
• This is t, the time for the change in velocity.
• When the cardboard passes through the second light gate the timer attached to it records this time.
• The final velocity, v = length of card / time on timer
• Then calculate acceleration, a = (v-u)/t
20
Q

What does the area under this velocity time graph give?

A

If positive area and negative area are subtracted it gives the displacement. If the total area is calculated it gives the distance travelled.

21
Q

What is work?

A

It is the measure of the energy used to move an object over a distance using a force.

22
Q

How can a space rocket be slowed down in space?

A

Reverse the thrusters to provide an unbalanced force backwards to slow you down.

23
Q

When does an object have kinetic energy?

A

When it is moving.

24
Q

When is work done?

A

When a force is exterted over a certain distance.

25
Q

What are the three effects a force can have?

A
• Change the speed of the object
• Change the direction of travel of the object
• Change the shape of the object
26
Q

How can you decrease friction?

A
• Decrease the area of the rubbing surfaces
• Make the rubbing surfaces smoother
• Push the rubbing surfaces together less
• Decrease the speed that the surfaces are rubbed together
• Lubricate/oil/ wax the surfaces
• Streamline the object
27
Q

What is conservation of energy?

A

Energy cannot be created or destroyed it can only be transferred from one type to another.

28
Q

What happens to the object at point X?

A

It changes direction

29
Q

What does this velocity-time graph show?

A

Constant acceleration

30
Q

What is meant by streamlining?

A

Streamlining is changing the shape of an object to reduce air/water resistance

31
Q

Name three scalar quantities

A
• Distance
• Time
• Speed
• Mass
• Energy
32
Q

An object travels at a constant speed of 10ms-1. What can be said about the forces on it?

A

The forces are balanced

33
Q

Explain why a projectile follows a curved trajectory.

A
• It has a constant horizontal velocity
• It has a constant vertical acceleration downwards due to gravity
34
Q

Explain how a seatbelt works in terms of Newton’s Laws.

A
• When a car travels at a constant velocity the forces on it are balanced. (Newtons 1st Law)
• If the brakes are applied they provide an unbalanced force that stops the car. (Newtons 2nd Law)
• The passengers continue to travel at a constant speed in a straight line. (Newtons 1st Law)
• The seatbelt provides an unbalanced backwards force to decelerate the passenger to zero without hitting the windscreen. (Newtons 2nd Law)
35
Q

What does the path a projectile takes look like?

A

Curve

36
Q

For a projectile fired horizontally, what would the vertical velocity time graph look like?

A

It would show a constant acceleration, a line of gradient = 9.8ms-2

37
Q

Explain the energy change as the sledge slides down the hill.

A
• At the start the sledge has potential energy.
• As it starts to slide down the hill it loses potential energy and gains kinetic energy
• At the bottom of the hill the sldge has no potential energy it has all been transferred to kinetic energy.
• At any point on the slope the potential energy + the kinetic energy = potential energy at the top of the slope.
38
Q

What causes friction?

A

Two surfaces rubbing together

39
Q

Explain how a satellite stays in orbit.

A

Satellite has a constant horizontal velocity.

Satellite has a constant vertical acceleration due to the gravitational field strength of the planet.

This gives a curved trajectory.

The planet is curved so the satellite remains in orbit.

40
Q

What does the gradient of the line on velocity - time graph represent?

A

The acceleration

41
Q

What does this velocity - time graph show?

A

Constant de-acceleration

42
Q

Describe a streamlined shape

A
• Low to the ground
• Smooth
• Have curves
43
Q

What does the area under the velocity-time graph give?

A

The distance travelled

44
Q

What is the difference between a vector and a scalar quantity?

A

A scalar needs size/magnitude to be described correctly. A vector needs size/ magnitude and direction to be described correctly.

45
Q

Explain how to measure the acceleration of the car using the equipment shown below and a stop watch.

A
• Car starts from rest so u = 0ms-1.
• When the car is released start the stop watch when it reaches the light gate stop the stop watch.
• This is t, the time for the change in velocity.
• When the cardboard passes through the light gate the timer attached to it records this time.
• Measure the length of the card with a ruler.
• The final velocity, v = length of card / time on timer
• Then calculate acceleration, a = (v-u)/t
46
Q

What is the weight of an object in freefall?

A

0 Newtons

47
Q

For a projectile fired horizontally, what would the horizontal velocity time graph look like?

A

Constant horizontal velocity - therefore a straight horizontal line.

48
Q

Describe how to calculate acceleration from a veocity - time graph.

A
• Pick two pints on the slope.
• u = initial speed-read it off the graph,
• v = final speed-read it off the graph,
• t = time to go from the initial to the final speed.
• Then use a = (v-u)/t
49
Q

If an object is projected horizontally or dropped, how can the vertical velocity just before it hits the ground be calculated?

A

Use a=(v-u)/t

u is 0ms-1

a is 9.8ms-2

v you are calculating

t is the time it falls for

a = (v-0)/t

v = at

50
Q

What is the difference between speed and velocity?

A

Speed is a scalar and is equal to distance divided by time. Velocity is a vector and is displacement divided by time, with a direction.

51
Q

A car is travelling at a constant velocity of 25ms-1, the engine is producing a force of 4000N. What is the size of the frictional forces acting on the car?

A

4000N backwards

52
Q

When does an object have potential energy?

A

When it is lifted through a height.

53
Q

Explain how a skydiver reaches terminal velocity.

A
• When the skydiver jumps out of a plane his initial vertical velocity is zero.
• His weight causes him to accelerate towards the ground. (Weight = Force = ma)
• As the skydivers velocity increases the air resistance upwards increases too.
• So the unbalanced force down becomes less, so there is less aceleration towards the ground. (Weight - air resistance = Unbalanced Force = ma)
• Eventually the weight downwards is equal and opposite to the air resistance upwards.
• This is a balanced force so the skydiver reaches terminal velocity.
54
Q

Describe how to measure average speed using the equipment below.

A
• Two light gates are connected to a timer.
• The car rolls down the slope.
• When the cardboard breaks the first lightgate beam it starts the timer. When the cardboard breaks the second lightgate beam it stops the timer.
• The timer records the time taken to go from the first to the second light gate.
• Measure the distance between the two light gates using a metre stick.
• Calculate the speed = distance between light gates / time on timer
55
Q

Explain how to use the equipment below to calculate the instantaneous speed of the car.

A
• Measure the length of the cardboard using a ruler.
• Roll car down the slope.
• When the cardboard breaks the beam it starts the timer connected to the light gate. When the cardboard has passed through the beam is remade and the timer stops.
• Speed = length of cardboard / time on timer
56
Q

Describe how to measure average speed.

A
• Mark a start line and a finish line.
• Measure the distance between the start and finish line with a ruler/metre stick.
• Start a stopwatch when the object crosses the start line and stop it when the object crosses the finish line.
• Calculate the average speed = distance between start and finish / time on stopwatch
57
Q

What is velocity?

A

Displacement travelled per second.