Forces 2 - weight, force diagrams, work done

Question 1

Define weight

Answer 1

Weight is the force acting on an object due to gravity.

Question 2

Why is the force of gravity so close to the earth.

Answer 2

The force of
gravity close to the Earth is due to the gravitational field around the
Earth.

Question 3

What does the weight of an object depend on

Answer 3

The weight of an object depends on the gravitational field strength
at the point where the object is.

Question 4

State the equation for weight

Answer 4

weight = mass x gravitational field strength

Question 5

State the equation that links weight, mass and gravitational field strength

Answer 5

W = mg
weight - in newtons N
mass in kg
gravitational field strength - g in newtons per kilogram N/kg

Question 6

What is an object’s centre of mass

Answer 6

An object’s centre of mass is the weight of an object (due to gravity) that can be considered to act at a single point

Question 7

why is mass a scalar quantity

Answer 7

Mass is a scalar quantity because it has no direction (magnitude only)

Question 8

Complete the sentence
The weight of an object is directly proportional to the ____ of the object

Answer 8

The weight of an object is directly proportional to the mass of the object

Weight ∝ Mass
(As mass doubles, weight also doubles)

Question 9

How can we determine an objects weight
How can weight be measured

Answer 9

Weight can be measured using a calibrated spring-balance (a newton meter)

Question 10

What is the gravitational field strength

Answer 10

The gravitational field strength is a measure of the force of gravity in a particular location
(the gravitational field strength depends on where you are)

Question 11

Define mass

Answer 11

The mass of an object tells us how much matter the object has in it.

Question 12

Why are forces vector quantities

Answer 12

Forces are vector quantities because they have both magnitude (size) and direction

Question 13

Define resultant force

Answer 13

The resultant force is a single force that has the same effect as all of the original forces acting together

Question 14

A man is applying a force of 20N acting to the right
A friction force of 10N is acting to the left
Work out the resultant force

Answer 14

Resultant force = 20 - 10 = 10N acting to the right
(DIRECTION IS NEEDED)

Question 15

Label the forces acting on a car travelling at a constant speed

Answer 15

air resistance/friction<-car-> driving force

Weight acting downward (e.g. 3cm arrow)
2 1.5 cm arrows for the wheels - normal contact force

Arrow for air resistance/friction should = length of arrow for driving force

Question 16

0 4 Hailstones are small balls of ice. Hailstones form in clouds and fall to the ground.

A hailstone falls from a cloud and accelerates.

Why does the hailstone accelerate?

Answer 16

there is a resultant force acting

(note:remember f=ma)

Question 17

Forces that are balanced should have be of the same length

Question 18

What happens, if the resultant force acting on an object is 0

Answer 18

If the resultant force acting on an object is zero, then all the forces are said to be balanced

Question 19

The skydiver is falling through the air at a constant velocity
The skydiver experiences a force of 800N acting downwards (this is his weight due to gravity)
At the same time the skydiver experiences an upward force of 800N due to air resistance
Calculate the resultant force

Answer 19

Resultant force = 800 - 800 = 0N -
In this case the forces are balanced

Question 20

Draw a free body diagram of:
The skydiver is falling through the air at a constant velocity
The skydiver experiences a force of 800N acting downwards
At the same time the skydiver experiences an upward force of 800N due to air resistance

Question 21

Describe the forces acting on an aeroplane flying at a constant velocity at a constant altitude

Answer 21

The weight of the aeroplane is acting downwards towards the Earth (due to gravity)

However, the aeroplane is at a constant altitude, therefore there must be a force the same magnitude as the weight but acting in the opposite direction.
That force is called lift

The aeroplane experiences a forward force provided by the engines, that force is called force
At the same time, the aeroplane also experiences the force of air resistance acting in the opposite direction

Because the aeroplane is moving at a constant velocity, the forward and backwards forces must be balanced

Question 22

Draw a free body diagram of an aeroplane flying at a constant velocity and constant altitude

Question 23

Vector diagrams
Two forces are acting on an object
One force has a magnitude of 10N and the other force has a magnitude of 8N.
The angle between the two forces is 30 degrees.
Calculate the resultant force

Answer 23

1cm = 1N
Use a ruler to draw a 10cm long arrow to represent the 10N force

Using a protractor - measure 30 degrees
Use a ruler to draw an 8cm arrow to represent the 8N force

Now create a parallelogram
To do that copy the 8cm line and position at the head of the 10cm force vector
Do the same for the 10cm line

Then draw a line from the tails of the force vectors to the other side of the parallelogram
Measure the length of the vector and work out the resultant force that it represents

Answer vector = 17.5cm = resultant forc1ce = 17.5N

Question 24

A force of 280N and a force of 320N are acting on an object
There is an angle of 20 degrees between the forces
Calculate the resultant force

Answer 24

1cm = 40N

Vector = 14.8cm = 592N

Question 25

Resolving forces
A 100N force is acting at an angle of 35degrees with the horizontal
Determine the horizontal and vertical components of this force

Answer 25

Scale = 1cm = 10N

Draw faint lines to show the horizontal and vertical axes

Using a protractor, measure 35 degrees from the horizontal

Use a ruler to draw the vector showing the 100N force (10 cm)

Now draw dotted lines from the head of the vector to the horizontal and vertical axes

At this point draw horizontal and vertical components

Use a ruler to determine the magnitude

Rub out any faint lines used to show the vectors in the final answer

Horizontal component = 8.3cm = 83N

Vertical component = 5.7N = 57N

Question 26

A 75N force is acting at an angle of 20 degrees with the horizontal
Determine the horizontal and vertical components of this force

Answer 26

Scale: 1cm = 10N

Horizontal component = 7cm = 70N

Vertical component = 2.5cm = 25N

Question 27

https://filestore.aqa.org.uk/sample-papers-and-mark-schemes/2021/november/AQA-84632H-QP-NOV21.PDF

question 7.5
look at diagram above q 7.4

Determine the magnitude and direction of the resultant force of the towbar on the
trailer by drawing a vector diagram

The resultant force of the towbar on the trailer has a horizontal component and a
vertical component.
horizontal force = 200 N
vertical force = 75 N
m

Magnitude of force = _______N
Direction of force = ____________N

Answer 27

https://filestore.aqa.org.uk/sample-papers-and-mark-schemes/2021/november/AQA-84632H-MS-NOV21.PDF

PAGE 19

Question 28

Define work

Answer 28

When a force causes an object to move through a distance, work is
done on the object.

Question 29

What happens when work is done against frictional forces acting on an object

Answer 29

Work done against the frictional forces acting on an object causes a
rise in the temperature of the object.

Question 30

Describe the energy transfer involved when work is done when a man is pushing a box

Answer 30

The chemical energy store in the man’s muscles has been transferred to the thermal energy store of the box

(the man is applying a forward force to the box, the force of friction is acting between the bottom of the box and the floor. The friction cause the temperature of the box to increase)

Question 31

What is transferred when force is used to move an object

Answer 31

Whenever a force is used to move an object, energy is transferred.

Question 32

equation that links work done, force and distance

Answer 32

W = F x s
Work done = Force x Distance

Work done - Joules - J
Force - Newtons
Displacement - METRES

distance must be in the line of action of the force
(e.g. a person walking up stairs - because weight is acting downwards - only vertical distance is relevant

Question 33

1 joule = ___

Answer 33

1 joule = 1 newton metre

Question 34

When is one joule of work done

Answer 34

One joule of work is done when a force of one newton causes a
displacement of one metre.

Question 35

A car is travelling with a velocity of 20m/s
The driver applies the brakes and the car comes to a stop
What happens when the car brakes?

Answer 35

During braking, the brake presses against the wheel

The force of friction now acts between the brake and the wheel

The kinetic energy store of the car is transferred to the thermal energy store of the brakes.

This causes the temperature of the brakes to increase and at the same time, the car slows down as it loses kinetic energy

Question 36

What type of energy store does a moving object have

Answer 36

A moving object has a kinetic energy store