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A Level Physics - LVI B > Mechanics and Materials > Flashcards

Flashcards in Mechanics and Materials Deck (51)
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1

State two conditions for a rod supported by two wires to be in equilibrium (2)

Resultant force zero
Resultant moment about any point zero

2

State three vector quantities (3)

Velocity
Acceleration
Force

3

State three scalar quantities (3)

Speed
Distance
Mass

4

State the three forces that will act on a helicopter that is moving horizontally (3)

Lift
Air resistance
Weight

5

How can force vectors be arranged to show that an object has constant velocity? (2)

Closed triangle of vectors
Forces are in equilibrium

6

What is the difference between a vector quantity and a scalar quantity? (1)

Vector has a direction
Scalar does not

7

What is meant by centre of gravity? (1)

The point in a body where the weight of the object appears to act

8

Define the moment of a force (1)

Product of the force and the perpendicular distance from the line of action of the force to the point

9

State the principle of moments (2)

Sum of the clockwise moments about a point is equal to the sum of the anticlockwise moments for a system in equilibrium

10

State and explain a feature of a crane that helps prevent it from falling over when lifting heavy things (2)

Counterweight
Provides a sufficiently large moment in the opposite direction

11

Why would a thin card give a more accurate measurement of g compared to dropping a tennis ball? (2)

Ball's acceleration will decrease
Air resistance affects cards less

12

What feature of a speed against time graph would show a constant acceleration? (1)

Constant gradient

13

Why does an object first accelerate after being dropped then reach a terminal velocity? (4)

Weight greater than air resistance
Therefore resultant force downwards
Air resistance increases with speed
Until resultant force is zero

14

Why would an apple hit the ground first if dropped with a leaf? (2)

Air resistance depends on surface area
Air resistance less on apple, therefore greater velocity

15

How can using an inclined ramp rather than free fall produce valid data on investigating a falling object's motion? (2)

Freefall is too fast
No accurate method to time freefall

16

On a distance against time graph, how would speed at a certain time/distance be worked out? (1)

Draw a tangent work out the gradient

17

For impulse and force, state whether each one is a vector or a scalar (2)

Impulse - vector
Force - vector

18

The rate of change of momentum of a body in free fall under gravity is equal to its.. (1)

Weight

19

On a force against time graph, what is the area under the graph equal to? (1)

The change in momentum of the body or impulse

20

In an inelastic collision, which quantity is not conserved? (1)

Kinetic energy

21

Use Newton's laws of motion to explain how molecules of gas exert a force on the wall of a container (3)

Force is exerted on molecule by wall
To change its momentum
Molecule must exert an equal but opposite force on wall
In accordance with Newton's third law

22

Describe how a trolley moving down a sloped track can have its speed measured experimentally (3)

Place piece of card on trolley of measured length
Card obscures light gate just before trolley strikes block
Calculate speed from length card and time the laser was obscured

23

Define density of a material (1)

Mass divided by volume

24

State Hooke's law (2)

The force needed to stretch a spring is directly proportional to the extension up to the limit of proportionality

25

What is meant by the elastic limit of a wire? (2)

The maximum amount that a material can be stretched and still return to its original length when the force is removed

26

Define a material's Young modulus and state the units (2)

Ratio of tensile stress to tensile strain
unit: Pa

27

Define tensile stress (1)

Force per unit cross-sectional area

28

Define tensile strain (1)

Extension per unit length

29

A wire is stretched beyond its elastic limit, explain why when the wire is unstretched, the line is parallel to original extension but does not return to zero (2)

Plastic deformation has produced permanent extension
Gradient is the same because identical forces between bonds

30

A pellet hits a wooden block hung by a string and is embedded in it, the wooden block reaches a certain height. A steel block is used and the pellet rebounds. Comparing energy and momentum changes, which block will reach higher (4)

As pellet rebounds, change in momentum of pellet is greater so change in momentum of block is greater
Initial speed of steel block is greater
Initial kinetic energy of steel block is greater
Therefore the height reached by the steel block is greater than with the wooden block