Unit 4 - Mechanics

Question 1

What is a scalar?

Answer 1

A quantity which only has a magnitude

Question 2

What is a vector?

Answer 2

A quantity which has a magnitude and a direction

Question 3

Where should the arrows start on a scale diagram?

Answer 3

At the centre of mass

Question 4

What is the resultant force?

Answer 4

The difference between forces that originates when there are multiple forces all acting on the same object

Question 5

If an object is stationary then the resultant force on the object is __ and the forces acting on it are ________

Answer 5

1. 0
2. Balanced

Question 6

How can you calculate the resultant force from a scale diagram?

Answer 6

Arrange the arrows top-to-tail and then use trigonometry to determine the resultant force

Question 7

What is resolving vectors?

Answer 7

The process of splitting up a resultant force into its separate components

Question 8

What two components are you most likely to resolve into?

Answer 8

Horizontal and vertical (unless the object is on a slope then the normal is included)

Question 9

Horizontal Force = ?
Vertical Force = ?

Answer 9

1. Resultant Force x cos(x)
2. Resultant Force x sin(x)

Question 10

What will happen to an object if the forces acting on it are balanced?

Answer 10

It will remain stationary or moving in the same direction at a constant speed

Question 11

What is a moment?

Answer 11

The turning effect of a force about a point (the pivot)

Question 12

What is the equation and unit for the moment?

Answer 12

Moment (Nm) = Force (N) x Distance (m)

Question 13

What angle does the force have to be to the distance when using the moments equation?

Answer 13

The force has to be perpendicular to the distance

Question 14

What do you do if the force is not perpendicular to the distance when calculating moments?

Answer 14

You can resolve the force into its horizontal and vertical component and the use the one which is at right angles to the distance

Question 15

What does it mean if the moments are balanced?

Answer 15

There is no resultant moment: sum of clockwise moments = sum of anticlockwise moments

Question 16

What is the line of action?

Answer 16

The line along which a force is considered to act

Question 17

What happens if the pivot point is on the line of action?

Answer 17

There is no turning effect

Question 18

What is torque?

Answer 18

The force produced when two equal and opposite forces which are parallel and act along different lines act about the same point

Question 19

What is the difference between speed and velocity?

Answer 19

Speed is a scalar quantity and velocity is a vector quanitity

Question 20

T/F: You can have negative velocity

Answer 20

True, because velocity is a vector it can be negative if acting in a negative direction

Question 21

What are the two main types of speed?

Answer 21

Average and instantaneous

Question 22

How do you determine the average speed from a distance-time graph?

Answer 22

Calculate the gradient of the whole graph

Question 23

How do you determine the instantaneous speed from a distance-time graph?

Answer 23

Draw a tangent to the curve at the point when you want to know the velocity and then calculate the gradient of that tangent

Question 24

T/F: Distance-time graphs can increase and decrease

Answer 24

False, distance-time graphs are always increasing because distance covered can never decrease

Question 25

Define acceleration

Answer 25

The rate of change of velocity

Question 26

Is acceleration a vector or a scalar?

Answer 26

A vector

Question 27

What can we infer about the velocity if there is uniform acceleration?

Answer 27

There is a constant change in velocity

Question 28

How can we calculate the acceleration from a velocity-time graph?

Answer 28

Calculate the gradient

Question 29

What is projectile motion?

Answer 29

The motion an object experiences as the result of a vertical force and no other horizontal force in a gravitational field

Question 30

How does an object move when experiencing projectile motion?

Answer 30

An object will maintain horizontal velocity whilst accelerating downwards

Question 31

What are Newton's 3 laws of motion?

Answer 31

1. An object will remain at rest or moving at a constant velocity unless acted upon by an external force 2. An unbalanced force acting on an object will cause it to accelerate in the direction of that force, this acceleration will be directly proportional to to the unbalanced force and inversely proportional to the mass of the object (F = ma) 3. If object A exerts a force on object B then object B exerts an equal and opposite force on object A

Question 32

Why do we draw free body diagrams?

Answer 32

We draw free body diagrams so that we can have a visual representation of the forces that are acting on an object and their magnitude and direction relative to each other and the centre of mass of the object

Question 33

What would happen if you are standing on scales in a lift and it is: a) moving down b) moving up c) stationary

Answer 33

a) The number of the scales will decrease as it uses springs to measure the reaction force of the person and, since weight can't change, in order for the lift to move down the upward force has to decrease b) It will increase for a similar reason as the reaction force has to increase in order for the lift to move up c) The number will stay the same as if the person was standing on normal ground as the person is stationary

Question 34

What is terminal velocity?

Answer 34

The maximimum velocity an object falling through a fluid can achieve

Question 35

Why does a skydiver reach a point where they are no longer accelerating?

Answer 35

This is because the velocity and the air resistance are directly proportional. As the velocity increases so will the air resistance which means that a point will be reached where the drag caused by the air resistance will be equal to the weight of the person so they will move downwards in a uniform manner

Question 36

Drag Force = ?

Answer 36

6 x Pi x Dynamic Viscosity x Radius of Sphere x Velocity

Question 37

What does Newton's third law state?

Answer 37

“If object A exerts a force on object B, then object B exerts an equal and opposite force on object A. Both forces are of the same type.”

Question 38

What is a third law pair?

Answer 38

Two objects that have a relationship due to Newton's third law because they have the same type of force acting on them

Question 39

What type of force is reaction force?

Answer 39

Electrostatic

Question 40

Why is reaction force electrostatic?

Answer 40

When a force is applied to the ground it pushes the atoms in the solid closer together, the opposing force is cause by the electrostatic repulsion between the nuclei of the two atoms

Question 41

What is impulse?

Answer 41

Force x Time (= Change in momentum)

Question 42

T/F: The rate of change of momentum is not equal to the unbalanced force applied

Answer 42

False: the rate of change of momentum is equal to the unbalanced force applied because if you link impulse and Newton's second law you end up with this equation: Force = (Mass x Change In Velocity) / Change In Time

Question 43

What are the three rules for calculating the momentum after a collision?

Answer 43

1) V1 = V2 2) M1V1 = M1V2 + M2V3 3) M1V1 = (M1 + M2)V3

Question 44

What is an elastic collision?

Answer 44

A collision in which all of the kinetic energy is conserved

Question 45

What is an inelastic collision?

Answer 45

A collision in which not all of the kinetic energy is conserved

Question 46

What do safety features in vehicles aim to do and why?

Answer 46

They aim to increase the time of the collision which decreases the force on the passengers

Question 47

What is work done equal to?

Answer 47

Energy transferred