Mod 3 Exam Q’s

Question 1

Name the object that experiences a force of magnitude W, but in the opposite direction to W

Answer 1

Earth

Question 2

According to a student, the normal contact force will equal the weight of an object when the object is stationary state why this is incorrect

Answer 2

The forces are not the same type of

Question 3

State, Newton’s second law of motion

Answer 3

Force is proportional to the change of momentum

Question 4

A ball speed just before hitting a ground is 14 m/s after the ball leaves the ground it speed reduces to 11 m/s
What is meant by elastic collision and explain how the change in velocity shows that this collision is not elastic?

Answer 4

Elastic collision is when total kinetic energy is conserved in a collision. Therefore velocity is also conserved as the velocity has changed. The energy is not constant. Therefore this is an inelastic collision.

Question 5

What does the area under a force against time graph represent?

Answer 5

Change of momentum

Question 6

What does the area under an acceleration time graph equal?

Answer 6

Velocity

Question 7

State archimedes principal

Answer 7

When an object is stationary, the weight of fluid is equal to the upthrust acting on the object

Question 8

Explain why the terminal velocity of a sand filled ball would be larger than a hollow ball of the same surface area and size

Answer 8

Because at term of velocity weight equals drag and as the sand ball has a greater weight and there will be greater drag due to the ball travelling at a greater speed therefore a greater terminal velocity

Question 9

Newton second law of motion

Answer 9

Forces proportional to the rate of change of momentum

Question 10

Trolley M collides with a trolley L . The mass of trolley is greater than the mass of trolley L then join together after the collision what can we say about the total force? Acting on the two trolley system during the collision. They are travelling in opposite direction

Answer 10

The total force acting on the two trolley system during the collision is zero. As when they collide t=0

Question 11

Two objects collide the collision is perfectly elastic. State the two quantities that are conserved.

Answer 11

Kinetic energy
Momentum

Question 12

A massive ball is released from rest above the ground
According to a student, the principle of conservation of momentum is violated because the ball gained momentum as it falls
Explain why the students observation is incomplete and is momentum conserved in this situation

Answer 12

The Earth has an equal and opposite momentum to the ball therefore momentum is conserved

Question 13

Define an elastic collision

Answer 13

A collision in which kinetic energy is not conserved

Question 14

A comment makes an inelastic collision with a small astroid in space
State two physical quantities which are conserved in this collision

Answer 14

Total energy and mass
Momentum

Question 15

When is the normal contact force greater than the weight?

Answer 15

In an elevator that is accelerating upward the normal force is greater than the persons ground weight. This is why the person may feel heavier

Question 16

Define work done by a force

Answer 16

Force x distance moved

Question 17

Explain how cars are designed to reduce impact

Answer 17

They have crumple zones they absorb some of the cars kinetic energy when they deform which would other but wise be transferred to the passengers time taken for the car to slow down which reduces the forces acting on the passengers
They have airbags which are cushions and they inflate very quickly on collisions. They protect the passengers by making passengers slow down more gradually therefore increasing the change of time and stopping passengers from hitting the dashboards.
They have seat belts which are designed to stretch slightly. They protect the passengers by holding the passengers in place stopping them from being thrown from their seats. They absorb some of the passengers kinetic energy by stretching and they increase the time that the passengers comes to a stop, therefore increasing the time .

Question 18

Explain some of the risks of safety features in cars

Answer 18

Seatbelt can cause bruising during a crash they can also strangle small children if the seatbelt is not secured properly therefore children must have booster seats
Airbags can be dangerous if not wearing a seatbelt as airbags inflate rapidly with a lot of force and if a passenger isn’t secured properly then the passenger can keep moving forward quickly as the car slows down and hit the airbag which can cause injury

Question 19

Define impulse and give equation

Answer 19

F x t = p
Impulse equals the change in momentum

Question 20

What type of material is polythene?

Answer 20

Ductile

Question 21

Why are the loading and unloading curves for rubber different gradients?

Answer 21

The energy released when the rubber is unloaded is less than the work done to stretch the rubber. This is because some of the elastic potential energy stored in the stretched rubber is converted to heat. This energy converted to heat per unit. Volume is given by the area between the load and unloading curves.

Question 22

What happens when stress is applied to a Brittle material?

Answer 22

Tiny cracks at the material surface get bigger and bigger until the material breaks completely. This is called brittle fracture

Question 23

Do stiff materials have a large or small young modulus

Answer 23

Large

Question 24

What is an indication of a strong material in a stress strain graph?

Answer 24

They have a higher breaking stress

Question 25

What is the area under a stress strain graph?

Answer 25

The elastic potential energy per unit volume so the energy stored per 1 m³ of a wire

Question 26

When finding young modulus in a practical, why should the test wire be thin?

Answer 26

It should be thin and as long as possible as the longer and thinner the wire the more extends for the same force therefore it reduces uncertainty

Question 27

Explain the effect of stress on a material

Answer 27

Stress starts to pull atoms apart from one another and eventually the stress becomes so great that the atoms separate completely material breaks

Question 28

Define hooks law

Answer 28

The extension or compression of a spring is proportional to the force applied provided the limit of proportionality has not been exceeded

Question 29

Explain elastic deformation in a material

Answer 29

When the material is put under detention, the atoms of the material are pulled apart from one another however the atoms can move slightly relative to the equilibrium positions without changing their position position in the material and once the load is removed the atoms can return to the equilibrium distance apart

Question 30

Explain plastic deformation in a material

Answer 30

This means material is permanently stretched and when the material is put under attention the atoms of the material are pulled apart from one another and some atoms in the material move position relative to one another therefore when the load is removed, the atoms do not return to the original position

Question 31

Define a couple

Answer 31

A pair of forces equal in size which act parallel to each other, but in opposite directions

Question 32

Define centre of mass

Answer 32

The single point that you can consider an object to act through

Question 33

How do you find the resultant force of two or more forces?

Answer 33

Resolve forces into the X and Y components
Add the X components
Add Y components
Then make a resultant force diagram and resolve