Forces and Energy

Question 0

What is a resultant force

Answer 0

When a number of different forces act at a point on an object, they add up to a resultant force. This is the single force that has the same effect as all the original forces combined Simply add up the forces acting in a straight line in that direction (if it points in the opposite direction you must take it away)

Question 1

What are forces?

Answer 1

Pushes and pulls Measured in Newtons

Question 2

What do forces do?

Answer 2

Cause an acceleration or, Cause a direction change or, Cause a change of shape or All of the above

Question 3

What happens if the resultant force is zero? Will the object not move, slow down speed up or stay at the same speed?

Answer 3

The object will continue at the same speed, or if it was already stationary it will remain so This is Newton’s first law of motion.

Question 4

How are force (resultant force) mass and acceleration related?

Answer 4

Force = mass x acceleration This is Newton’s second law

Question 5

What are forces measured in?

Answer 5

Newtons (N)

Question 6

What is mass measured in?

Answer 6

kilograms, kg

Question 7

What is weight measured in?

Answer 7

Newtons, N It is the force due to gravity

Question 8

What is speed measured in?

Answer 8

meters per second m/s

Question 9

What is acceleration measured in?

Answer 9

meters per second per second m/s2

Question 10

What is speed?

Answer 10

A measure of how fast something is moving. It is the distance moved in a certain amount of time.

Question 11

What is velocity?

Answer 11

Speed is how fast you are moving Velocity is how fast you are moving is a particular direction. It is a VECTOR quantity. Examples 30km/h North

Question 12

What does the gradient (how steep the line is) of a distance time graph tell you?

Answer 12

The speed the object is moving at The steeper it is the faster it is moving

Question 13

What is deceleration?

Answer 13

Acceleration in the opposite direction to the motion (negative acceleration)

Question 14

What is acceleration

Answer 14

Rate at which velocity changes Change in velocity / time

Question 15

What does the gradient (how steep) of a velocity time graph represent?

Answer 15

Acceleration

Question 16

What forces act on a car when it is moving?

Answer 16

Resistance, air resistance, driving force You may also have identified , weight and the normal reaction force from the road on the car

Question 17

What is the resultant force of a car travelling at constant speed?

Answer 17

Zero

By Newton’s First Law if an object is travelling at constant speed there can be no resultant force acting on it. Otherwise it would be accelerating.

Question 18

The same constant breaking force is used to stop a car; whatever speed it is travelling at to start with.

Explain what happens to the car’s stopping distance for higher speeds.

Answer 18

It will increase

In fact the braking distance goes up x4 when the velocity goes up x2.

Question 19

What is the total stopping distance of a car made up of?

Answer 19

Thinking distance (reation time)

+

Braking distance

Question 20

Which factors affect thinking distance

Answer 20

Tired

Drugs

Distractions (playing music, using mobile phone, chatting)

Age

Question 21

Which factors affect braking distance?

Answer 21

Road conditions (ice, snow rain, type of road)

Condition of the tyres

Condition of the brakes

Question 22

How much (approximately) does the stopping distance increase when the speed increases from 30mph to 50mph

Answer 22

at 30mph stopping distance is 23m

at 50mph it is 53m

increase is 30m

Question 23

What is the definition of weight?

Answer 23

Force on a object due to gravity

Weight (N) = Mass (kg) x Gravitation Field Strength (10 N/kg on Earth)

Question 24

As an objects fall through air which forces will act on it?

Answer 24

Gravity and Air resistance

The faster the object fall the larger the air resistance will become

Question 25

What is Terminal Velocity?

Answer 25

When the forces on an object, which is falling, reach an equilibrium (air resistance = weight) the object will no longer accelerate and has reached it’s Terminal velocity

As an object falls through the air (or fluid) it experience a resistive force called DRAG

The faster the object falls the larger this force becomes

It will continue to accelerate until the DRAG force is equal to the downward force

The object cannot accelerate now and has reached TERMINAL VELOCITY

Question 26

How does a parachute reduce a skydiver’s terminal velocity?

Answer 26

Parachute creates a large air resistance (suddenly)

This force is much greater than the weight cause a new resultant force which decelerates the skydiver

As the speed decreases so does the air resistance on the parachute until a new lower terminal velocity is reached

Question 27

What is the limit of proportionality?

Answer 27

The point beyond which increasing the force will cause a permament deformation. In other words the spring will no longer return to it’s original shape

Question 28

What is Hooke’s Law?

Answer 28

Force = Sping constant x Extension

F = k x e

Force applied to an object is directly proportional to the extension

Question 29

What is the definition of work done?

Answer 29

Another way of saying how much energy is transferred

It is measured in Joules

Work done = Force x distance

W = F x d

Question 30

What is the definition of Power

Answer 30

How much work is done (or energy transferred) in a given time

In other words, a powerful machine can do a lot of work in a short space of time.

Power (W) = work done (J) / time (s)

or

Power (W) = energy transferred (J) / time (s)

It is measured in Watts (W)

Question 31

What is Gravitational Potential Energy?

Answer 31

The energy an object possesses due to it’s position in the graviational field. In otherwords how far off the ground it is. The higher it is the more energy it possesses

GPE = mass x gravitational field strength x change in height

GPE = m x g x h

Question 32

What is Kinetic Energy?

Answer 32

The energy an object possesses due only to it’s motion

KE = ¹/₂ mass x speed²

KE = ¹/₂ m x v²

Question 33

What is the law of conservation of energy?

Answer 33

Energy cannot be created or destroyed

It can only be transferred from one type to another

Question 34

What 2 things does momentum depend upon?

Answer 34

The mass of an object

The velocity of the object (remember that object which move towards each other at the same speed will not have the same velocity as one will be negative)

momentum = mass x velocity

Unit for momentum are

kg m/s