Mechanics Flashcards
The area under a velocity- time graph is…
…Displacement
The gradient of a stress- strain graph is…
… Young modulus.
The gradient of a force-load graph is…
…. force constant.
State two scalar quantities in physics that have the same unit as each other.
- Energy and work done.
- pressure and stress
Horizontal component on a projectile.
- Horizontal component of the velocity is constant.
- There is no horizontal force.
Circumference of a circle.
2 x Pie x r
Explain what is meant by the gravitational potential energy.
is the work done in moving a unit mass from infinity to that point.
Force exerted on ground during impact.
- F=ma
- F= m x (v-u/t)
Vector quantity
has both direction and magnitude
If an object is in equilibrium…
…the net force is zero
Define force constant
The force per unit extension.
Why does the acceleration of the trolley decrease…
the resultant force is smaller.
Centre of gravity
A point where the entire weight of the object appears to act.
Moment of a force
force x perpendicular distance from line of force
State two conditions necessary for the rod to be in equilibrium. (moments)
- Net force=0
- Net moment=0 (clockwise moments= anticlockwise moments)
1 Watt
1 joule of energy transferred per 1 second.
Similarity of distance and displacement
Both measured in metres
Difference between distance and displacement
One is scalar, one is a vector
The gradient of a velocity-time graph..
…is acceleration
In an experiment of free fall, explain why g may be less then 9.81
- reaction time of student
- displacement isn’t precise enough
Sky diver jumps- immediately after jumping…
- Only force is the weight/drag = 0
- net force = weight
- acceleration = g/9.8(1 m s-2)
Sky diver before terminal velocity…
- Drag increases (with speed)
- drag prop. speed^2
- Net or resultant or total force decreases
- weight > drag
- Acceleration is less than g
Sky diver at terminal velocity….
- weight = drag
- net force = 0
- acceleration = 0
- constant speed or velocity
In the final stage pf the fall, the skydiver is falling through air at a constant speed. The skydiver’s KE doesn’t change even though there is a decrease in the GPE. State to what happens to this loss of GPE.
Transformed to heat/thermal (energy)
Define work done.
force x distance moved in the direction of the force
Define Power.
The amount of energy transformed from one form to another per second. (P= work done/time)
Explain why the effciency of mechanical device can never be 100%
energy is always lost as heat.
Principle of moments
For equilibrium of an object the sum of clockwise moments about a point = sum of anticlockwise moments about the same point. clockwise moment(s) = anticlockwise moment(s)
State and how explain how the pressure would change, if the same screw was secured much closer to the pivot.
- Pressure is greater
- because the force/F is larger (to provide the same moment)
Define the ultimate tensile strength of a material.
Maximum stress material can withstand (before fracture)
State Hooke’s Law.
extension (or compression) is proportional to force (as long as elastic limit is not exceeded)
-F=kx
State the main characteristics of rubber (stress-strain graph)
- The material is elastic / strain is zero when stress is removed / returns to its original shape when force is removed / there is no plastic deformation
- It does not obey Hooke’s law
- The loading and unloading graphs are different
- Hytheris
Define velocity
velocity = rate of change of displacement
State the physical properties of a brittle metal (stress-strain graph).
- The material is brittle.
- The material is also elastic.
- No plastic deformation.
A tennis ball and a golf ball are dropped out of an upper window at the same time. The golf ball has greater mass. Which of these two balls reaches greater terminal velocity.
- The golf ball experiences greater drag (at terminal velocity to equal its larger weight) (AW)
- Drag increases with speed/drag proportional to  v^2
- The golf ball takes longer time to reach its terminal velocity or the golf ball accelerates for longer time
- The golf ball (has greater terminal velocity)
The driver wears a seat belt. Describe and explain how a seat belt reduces the force on a driver during the impact in an accident.
- The time taken (for the driver) to stop is more or distance travelled (by the driver) is greater.
- F = ma meaning a decreases (hence F is smaller)
- Fx = KE meaning KE is the same (hence F is smaller)
- F= p/ t meaning p is the same (hence F is smaller)
A crate is pushed along a rough horizontal surface at a constant speed. State what happens to the work done on the crate.
(Work done against friction generates) heat / thermal energy / internal energy
The vertical upward force on the spaceship stays constant. Explain why the acceleration of the spaceship increases after lift off.
The mass/weight (of spaceship) decreases as it loses fuel.
Area under a force-extension graph…
…Elastic Potential Energy
Two factors that affect the magnitude of drag force acting on object falling through air.
- The surface area
- Velocity
- ‘Aerodynamic” shape
Explain what is meant by gravitational potential energy without using an equation.
GPE linked to ‘position’ / height (in a gravitational field)
A student wants to carry out an experiment to determine the input power to a small electric motor without using electrical meters. The motor is used to lift light loads. The efficiency of the motor is 15%. Describe how this student can determine the input power to the motor.
-Mass obtained using a balance / scales
-Weight / load obtained using a newtonmeter / spring
balance
-Distance / height obtained using a ruler / metre stick /
measuring tape
Time obtained using a clock / (stop)watch / timer or light- gate and timer or light-gate and data-logger
(output power =) ‘mass x g x distance’/time or ‘weight distance/time’ or ‘weight x speed’
input power = output power/0.15
The acceleration of an electron decreases as its velocity increases. Why?
The mass (of the electron) increases as its speed approaches the speed of light
Describe one example where elastic potential energy is stored.
stretched elastic band
Work done stretching a spring equation(s)…
1/2x F x (x)
or
1/2 x k x (x)^2
Pressure units
kg m^-1 s^-2
Power units
kg m^2 s^-3
