Mod 3 Exam Q’s Flashcards
Name the object that experiences a force of magnitude W, but in the opposite direction to W
Earth
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
The forces are not the same type of
State, Newton’s second law of motion
Force is proportional to the change of momentum
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?
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.
What does the area under a force against time graph represent?
Change of momentum
What does the area under an acceleration time graph equal?
Velocity
State archimedes principal
When an object is stationary, the weight of fluid is equal to the upthrust acting on the object
Explain why the terminal velocity of a sand filled ball would be larger than a hollow ball of the same surface area and size
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
Newton second law of motion
Forces proportional to the rate of change of momentum
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
The total force acting on the two trolley system during the collision is zero. As when they collide t=0
Two objects collide the collision is perfectly elastic. State the two quantities that are conserved.
Kinetic energy
Momentum
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
The Earth has an equal and opposite momentum to the ball therefore momentum is conserved
Define an elastic collision
A collision in which kinetic energy is not conserved
A comment makes an inelastic collision with a small astroid in space
State two physical quantities which are conserved in this collision
Total energy and mass
Momentum
When is the normal contact force greater than the weight?
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
Define work done by a force
Force x distance moved
Explain how cars are designed to reduce impact
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 .
Explain some of the risks of safety features in cars
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
Define impulse and give equation
F x t = p
Impulse equals the change in momentum
What type of material is polythene?
Ductile
Why are the loading and unloading curves for rubber different gradients?
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.
What happens when stress is applied to a Brittle material?
Tiny cracks at the material surface get bigger and bigger until the material breaks completely. This is called brittle fracture
Do stiff materials have a large or small young modulus
Large
What is an indication of a strong material in a stress strain graph?
They have a higher breaking stress
What is the area under a stress strain graph?
The elastic potential energy per unit volume so the energy stored per 1 m³ of a wire
When finding young modulus in a practical, why should the test wire be thin?
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
Explain the effect of stress on a material
Stress starts to pull atoms apart from one another and eventually the stress becomes so great that the atoms separate completely material breaks
Define hooks law
The extension or compression of a spring is proportional to the force applied provided the limit of proportionality has not been exceeded
Explain elastic deformation in a material
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
Explain plastic deformation in a material
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
Define a couple
A pair of forces equal in size which act parallel to each other, but in opposite directions
Define centre of mass
The single point that you can consider an object to act through
How do you find the resultant force of two or more forces?
Resolve forces into the X and Y components
Add the X components
Add Y components
Then make a resultant force diagram and resolve
