Mechanics Flashcards

1
Q

What are the vector quantities?

A

Displacement, velocity, acceleration, force, momentum

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2
Q

How do you calculate displacement from a velocity time graph?

A

Calculate the area under the graph

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3
Q

How do you calculate displacement from a velocity time graph if it is curved?

A

Use the count the squares method

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4
Q

What is the definition of stopping distance?

A

Total distance travelled from when the driver first sees the reason to stop to when the vehicle stops.

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5
Q

What is the equation for stopping distance?

A

Stopping distance = thinking distance + braking distance

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6
Q

What is the definition of thinking distance?

A

Distance travelled between moment when you first sees a reason to stop, to the moment when you use the brake.

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7
Q

What is the definition of braking distance?

A

The distance travelled from the time the brake is applied until the vehicle stops.

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8
Q

What factors affect stopping distance?

A

Speed of vehicle, condition of brakes, condition of tires, condition of the road, weather conditions, alertness to the driver.

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9
Q

What is the equation for thinking distance?

A

Thinking distance = speed x reaction time

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10
Q

How would you calculate braking distance?

A

Use SUVAT equations

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11
Q

How would you draw a scale drawing?

A

Decide on a scale for the length of vectors and use a protractor to draw angles accurately. Measure the length of the unknown vector and convert to Newtons using the scale.

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12
Q

What is the definition of drag?

A

A frictional force that resists the motion of an object through a fluid.

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13
Q

Define a Newton

A

The force that causes a mass of
one kilogram to have an acceleration of one metre per second squared.

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14
Q

When and why is F=ma no longer valid?

A

Due to Einstein’s Theory of Special Relativity, mass increases if the object is travelling very close to the speed of light.

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15
Q

Define centre of mass of an object

A

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

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16
Q

Where is the centre of gravity for a regular shaped object?

A

Where its lines of symmetry meet.

17
Q

Where does the centre of mass act for a uniform object?

A

At the centre of the object.

18
Q

Define a moment

A

Moment = force x perpendicular distance to the line of action of the force from the axis or point of rotation

19
Q

Define the principle of moments

A

For a body in equilibrium, the sum of the anticlockwise moments about any point is equal to the sum of the clockwise moments about that same point.

20
Q

Define a couple

A

A pair of forces equal in size acting parallel to each other but in opposite directions.

21
Q

What features must a couple have?

A

Forces must be equal in magnitude
Forces must be parallel but opposite in direction
Forces must be separated by a distance d

22
Q

Define torque of a couple

A

Torque of a couple = size of one of the forces x perpendicular distance between the forces

23
Q

Define work done

A

Work done = force x displacement in the direction of the force

24
Q

Define a Joule

A

1 Joule is equal to the work done by a 1 Newton force moving an object through 1 metre.

25
Q

Define the principle of conservation of energy

A

Energy cannot be created or destroyed, it transfers between different forms.

26
Q

Define power

A

Rate of energy transfer

27
Q

Define a Watt

A

Work done of 1 Joule in 1 second

28
Q

Why is no mechanical device 100% efficient?

A

There is always a waste heat due to work done against resistive forces such as friction.

29
Q

Define pressure

A

Normal force per cross sectional unit area

30
Q

Define Pascal

A

1 Newton per metre squared

31
Q

What do the letters represent in the equation p= ρgh?

A

p - pressure at the base of the column
ρ - density of the fluid
h - height on the column

32
Q

State archimedes principle

A

For an object fully or partly submerged in a fluid, there is a force of upthrust equal to the weight of the fluid displaced.

33
Q

What happens to wood released from the bottom of a tank full of water?

A

It will eventually float, as the wood speeds up the drag will increase, it may reach terminal velocity if
W + D = U before the surface.

34
Q

Write an equation for the forces acting on wood when it floats