Mechanics

Question 1

What is energy?

Answer 1

The ability to do work

Energy is often difficult to define, but this is a common definition.

Question 2

How many types of energy are there?

Answer 2

Two types:
* Kinetic energy
* Potential energy

Question 3

What is kinetic energy?

Answer 3

The energy of movement

Kinetic energy depends on mass and velocity.

Question 4

What is potential energy?

Answer 4

The energy of position

It can be gravitational or elastic.

Question 5

What is the principle of conservation of energy?

Answer 5

The total amount of energy in a closed system is fixed.

Question 6

What is elastic potential energy?

Answer 6

Energy stored in a material as it becomes deformed.

Question 7

What is efficiency in a system?

Answer 7

The proportion of total energy converted into useful work.

Question 8

How is power defined?

Answer 8

The rate of flow of energy.

Question 9

What is the unit of power?

Answer 9

Watts (W), where 1 Watt = 1 Joule/second.

Question 10

What is the formula for power?

Answer 10

P = E/t

Where P = power, E = energy, and t = time.

Question 11

What is the difference between scalars and vectors?

Answer 11

Scalars have magnitude; vectors have magnitude and direction.

Question 12

What does a straight line with a positive gradient on a velocity-time graph indicate?

Answer 12

Constant acceleration.

Question 13

What is equilibrium in a system?

Answer 13

The sum of all forces acting on the system is equal to zero.

Question 14

List the variables in constant acceleration equations.

Answer 14

u = initial velocity, v = final velocity, s = displacement, a = acceleration, t = time.

Question 15

What is projectile motion?

Answer 15

Motion of an object under freefall, with only gravity acting on it.

Question 16

What is the horizontal component of acceleration in projectile motion?

Answer 16

Zero, as there are no horizontal forces acting.

Question 17

What mathematical principle is used to combine the horizontal and vertical components of motion?

Answer 17

Pythagoras’ theorem

This theorem relates the lengths of the sides of a right triangle to calculate the hypotenuse.

Question 18

What is the centre of mass of an object?

Answer 18

The point through which the weight of the object acts.

Question 19

What is a moment?

Answer 19

The rotational effect of a force.

Question 20

How is a moment calculated?

Answer 20

Force times perpendicular distance

Question 21

What happens when a force is applied through the centre of mass?

Answer 21

It has a zero moment (turning effect).

Question 22

What is the ‘principle of moments’?

Answer 22

For a system in equilibrium, the sum of the clockwise moments equals the sum of the anti-clockwise moments.

Question 23

List the three conditions for a system to be in equilibrium.

Answer 23

• The sum of the horizontal forces is equal to zero
• The sum of the vertical forces is equal to zero
• The sum of the moments is equal to zero

Question 24

What is a ‘couple’ in physics?

Answer 24

A pair of equal forces, equidistant from a pivot, and acting in the same direction, with regard to their rotational effect

Question 25

What is momentum defined as?

Answer 25

The product of the mass and the velocity of an object.

Question 26

What is the law of conservation of momentum?

Answer 26

For a closed system, the total momentum remains constant.

Question 27

What distinguishes elastic collisions from inelastic collisions?

Answer 27

In elastic collisions, both momentum and kinetic energy are conserved; in inelastic collisions, momentum is conserved, but some kinetic energy is lost.

Question 28

What is the normal reaction force?

Answer 28

The force exerted by a surface that supports the weight of an object resting on it.

Question 29

What does Newton's First Law state?

Answer 29

A body will remain in its present state of rest or motion unless acted on by a force.

Question 30

What is the relationship described in Newton's Second Law?

Answer 30

The net force acting on an object is directly proportional to its rate of change of momentum.

Question 31

What does Newton's Third Law state?

Answer 31

For every action, there is an equal and opposite reaction.

Question 32

What are the two ways that a pair of forces described by N3L are equal?

Answer 32

1. Equal magnitude 2. Same type (push responds to push etc.)

Question 33

What are the two ways that a pair of forces described by N3L are opposite?

Answer 33

1. Opposite direction 2. They act of different bodies

Question 34

What is impulse?

Answer 34

Change in momentum.

Question 35

How can impulse be calculated on a force-time graph?

Answer 35

By finding the area under the graph.

Question 36

What is the unit of momentum?

Answer 36

Newton seconds or kilogram metres per second.