P3 - Using Physics

Question 1

What is the moment of a force?

Answer 1

A measure of the turning effect of a force on an object.

Question 2

How is the moment of a force calculated?

Answer 2

force x perpendicular distance from the line of action of the force to the pivot

Question 3

Give two ways in which the moment of a force can be increased.

Answer 3

• Increase the force

- Increase the perpendicular distance

Question 4

What is the centre of mass of an object?

Answer 4

The point where its mass is concentrated.

Question 5

Where is the centre of mass of an object that is suspended from a fixed point?

Answer 5

The centre of mass is directly beneath the point of suspension.

Question 6

Where is the centre of mass of a symmetrical object?

Answer 6

Along the axis of symmetry.

Question 7

What is the relationship between the moments of the forces acting on an object that isn’t turning?

Answer 7

The sum of anticlockwise moments = The sum of clockwise moments (ie. W1d1 = W2d2)

Question 8

How is the weight of the first object calculated with moments?

Answer 8

W1 = W2d2 / d1

Question 9

Give three ways in which an object can be made more stable.

Answer 9

• Increasing the width of the base.
• Making the centre of mass lower.
• Bolting the object to the floor.

Question 10

What will make a body topple over when tilted?

Answer 10

If the line of action of its weight is outside its base.

Question 11

What are the moments of the forces when an object topples over?

Answer 11

The resultant moment about the point of turning is not zero.

Question 12

What is pressure?

Answer 12

Force divided by the area which the force acts on.

Question 13

What is the unit of pressure?

Answer 13

The Pascal, Pa. (1 N/m2)

Question 14

What happens to the pressure in a fluid?

Answer 14

The pressure acts equally in all directions.

Question 15

How does a hydraulic pressure system work?

Answer 15

• Hydraulic fluid into the upper or lower part of a chamber to make the piston move in or out of the cylinder.
• The force exerted is transmitted to other parts of the system.

Question 16

Why are liquids used in hydraulic systems?

Answer 16

• Liquids are virtually incompressible so the volume doesn’t change.
• The whole force can be transmitted to the other parts.

Question 17

How does a hydraulic car jack work?

Answer 17

• The handle being pressed down forces hydraulic fluid out of a narrow cylinder into a wide cylinder.
• The pressure of the fluid forces the piston in the wider cylinder outwards.
• The piston forces the pivoted lever to raise the car.

Question 18

Why is the second force in a hydraulic car jack greater?

Answer 18

The area of the piston is greater.

Question 19

How can an object moving at a constant speed be accelerating?

Answer 19

If the motion is circular.

Question 20

Why is an object moving in a circular motion said to be accelerating?

Answer 20

• Velocity is dependent on direction as is acceleration.

- The velocity is changing as the direction is changing.

Question 21

What is centripetal acceleration?

Answer 21

The acceleration towards the centre of the circle of an object that is moving round the circle.

Question 22

What does the centripetal force depend on?

Answer 22

• Mass
• Speed
• Radius of the circle

Question 23

What is centripetal force?

Answer 23

The name of a resultant force acting on a circle moving round an object.

Question 24

What affects the time period of a pendulum?

Answer 24

Its length.

Question 25

How is the time period of a pendulum measured accurately?

Answer 25

The average time of 20 oscillations.

Question 26

How is a playground swing different to a pendulum?

Answer 26

• Friction at the top of the swing slows it.

- Air resistance slows it.

Question 27

What is the equilibrium position of a pendulum?

Answer 27

The point at which the pendulum is fastest and nearest the ground.

Question 28

What is the amplitude of an oscillating object?

Answer 28

The distance from the equilibrium position to its highest point.

Question 29

What is the time period of a pendulum?

Answer 29

-The time to one of the highest points and back.
or
-The time between successive passes in the same direction through the equilibrium.