Standard Answers Flashcards
Newtons Second Law.
Resultant force on an object is directly proportional to the rate of change of momentum and occurs in the same direction as the change in momentum.
Use Newtons Third law to explain the impulse received by A and B.
- Force exerted on A due to B is equal in magnitude and opposite in direction.
- Time of contact is the same and Impulse is FT
- Hence the Impulses are equal in magnitude and opposite in direction
Define Impulse.
Force x time in which the force acts
Define linear momentum.
mass x velocity
Why is Linear momentum a vector?
- Velocity is a vector
- The product of a scalar and a vector is a vector.
State the principle of conservation of momentum.
Total momentum is conserved provided no external forces are applied
Which conditions must be upheld for Newtons 3rd Law?
- Forces must act on different objects
- Forces must be equal in magnitude, type and opposite in direction
Why does speed of an object undergoing circular motion remain constant even with a resultant force acting on it?
- Resultant force is at right angles to direction of motion.
- No work is done by the force.
- KE and speed therefore constant
What is a Geostationary Orbit?
- Always vertically above the same point on earth
- Located above the equator with the same time period as earth
- Velocity of satellite parallel to velocity of a point on the surface at all times.
Describe the pattern of uniform field lines.
The field lines are parallel and equally spaced.
What are the benefits of Geostationary orbits?
- Receiving dish on earth can be kept in the same position as satellite stays above the same point on earth.
- Allowing it to be used for radio communications, TV signals etc
What is SHM?
- Acceleration proportional to displacement from equilibrium.
- This acceleration is always directed towards the equilibrium position
Difference between frequency and angular frequency?
Frequency is the number of oscillations per unit time. Angular frequency is 2pi x frequency.
What is resonance?
- Occurs when the driving frequency matches the natural frequency
- The amplitude of vibrations is then maximum due to maximum energy transfer from driver to the system.
What are the effects of damping on resonance?
- Smaller amplitude of vibrations
- Also slightly reduces the frequency which corresponds to max amplitude
What is Thermal equilibrium?
There is no net heat flow between the objects in contact and they are at the same temperature
Define internal energy
The sum of the randomly distributed KE and PE of the atoms/molecules in the system
Difference between ideal gas and real gas?
- Internal energy is the the sum of the randomly distributed KE and PE of the atoms/molecules in the system
- In an ideal gas all the internal energy is kinetic as it is assumed there is no attraction between molecules
- In a real gas some of this energy is potential energy
State some of the conclusions of molecules from observing smoke particles under a microscope.
- Movement of smoke particles caused by the molecules of the gas moving randomly
- Gas molecules not visible so they are much smaller.
- Smoke is continuously moving meaning the molecules are continuously moving the
State the kinetic model assumptions.
- Collisions of molecules with walls are perfectly elastic.
- Force between molecules is negligible except during collisions
- Large number of particles moving rapidly and randomly
- Volume of molecules is negligible compared to the volume of the container.
- Time during a collision is negligible compared to time between collision.
How does a gas exert pressure on the container walls?
- There are many collisions with the molecules and the wall, causing a change in momentum.
To change momentum the wall must have provided a force as the rate of change of momentum is proportional to the force exerted. - by Newtons 3rd law, an equal force must have been applied in the opposite direction
- Pressure= Sum of all forces/area of wall
Why does force on wall increase with temperature?
- Speed of gas molecules increase
- More frequent collisions
- The change in momentum is also larger
- So total force exerted in the container increases.
Why must the volume of gas increase if the pressure is to remain constant as it is heated.
- As temperature increases, the speed of the molecules increases resulting in a greater rate of collisions and greater changes in momentum.
- For a constant pressure, fewer collision per unit time are needed.
- Can be achieved by increasing volume as the molecules will need to travel a greater distance between collisions
Describe how the scattering experiment provided evidence for the existence, charge and size of the nucleus.
- Most went straight through and some deviated through small angles, showing the atom is mostly empty space.
- A very small number scattered through large angles, showing the existence of a tiny positive nucleus.
- Size of nucleus is about 10^-14m