Flashcards in Section 3 - Mechanics and Materials Exam Questions Deck (47)

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1

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

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Resultant force zero

Resultant torque about any point zero

2

## State three vector quantities (3)

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Velocity

Acceleration

Force

3

## State three scalar quantities (3)

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Speed

Distance

Mass

4

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

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Lift

Air resistance

Weight

5

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

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Closed triangle of vectors

Forces are in equilibrium

6

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

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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)

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Counterweight

Provides a sufficiently large moment in the opposite direction

11

## A stationary car and trailer are attached by a towbar, F is the force exerted by the towbar on the trailer. What happens to the magnitude and direction of F when the car moves forward? (3)

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Force must have a horizontal component

F increases in magnitude

F acts at an angle towards the car

12

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

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Ball's acceleration will decrease

Air resistance affects cards less

13

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

### Constant gradient

14

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

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Weight greater than air resistance

Therefore resultant force downwards

Air resistance increases with speed

Until resultant force is zero

15

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

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Air resistance depends on shape

Air resistance less on apple, therefore greater velocity

16

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

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Freefall is too fast

No accurate method to time freefall

17

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

### Draw a tangent

18

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

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Impulse - vector

Force - vector

19

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

### Weight

20

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

### The change in momentum of the body

21

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

### Kinetic energy

22

## A person is kicking a football, discuss the radial force on the knee joint before impact and during the impact (2)

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Before impact: radial pull on knee joint due to centripetal acceleration of boot

During impact: radial pull reduced

23

## State the relationship between the force acting on a body and the body's momentum (1)

### Force is equal to the rate of change of momentum

24

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

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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

25

## A deep space probe ejects a capsule explosively, and immediately after the probe moves at a greater speed. Discuss how conservation of momentum and energy apply in this instance (6)

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Momentum:

Momentum conserved because there are no external forces acting on the overall system

During the explosion there are equal and opposite forces acting between the probe and the capsule

Because momentum is a vector, the capsule must move along the original line of movement

Energy:

Total energy is always conserved in any physical process

Energy may be converted from one form to another

In the explosion, some chemical energy is converted to kinetic energy

26

## A ball rolls towards a footballer and is then kicked, if the ball had a higher initial speed and received the same impulse, discuss how it may differ (3)

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Final speed would be lower

Initial momentum would be greater

Change in momentum is the same

27

## A motor is used to lift a metal block vertically at constant speed. Describe an experiment to check whether the speed is constant (2)

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Mark out equal distances along height being raised

Measure time taken to travel each of these distances

28

## Explain how the output power of the motor is calculated, state any measurements made (3)

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Find work done by motor from gain in potential energy of metal block

Divide work done by time to find power

Measurements: mass of block, height block has risen and time taken

29

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

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Place piece of card on trolley of measured length

Card obscures light gate just before trolley strikes block

Calculate speed from length of time obscured

30