Section 3 - Mechanics and Materials Exam Questions Flashcards Preview

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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)

Resultant force zero
Resultant torque 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

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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

State an advantage and disadvantage of wind power in comparison to fossil fuel (2)

Causes no air pollution
Wind is intermittent