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Mechanics Flashcards

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1
Q

The area under a velocity- time graph is…

A

…Displacement

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2
Q

The gradient of a stress- strain graph is…

A

… Young modulus.

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3
Q

The gradient of a force-load graph is…

A

…. force constant.

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4
Q

State two scalar quantities in physics that have the same unit as each other.

A
  • Energy and work done.

- pressure and stress

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5
Q

Horizontal component on a projectile.

A
  • Horizontal component of the velocity is constant.

- There is no horizontal force.

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6
Q

Circumference of a circle.

A

2 x Pie x r

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7
Q

Explain what is meant by the gravitational potential energy.

A

is the work done in moving a unit mass from infinity to that point.

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8
Q

Force exerted on ground during impact.

A
  • F=ma

- F= m x (v-u/t)

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9
Q

Vector quantity

A

has both direction and magnitude

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10
Q

If an object is in equilibrium…

A

…the net force is zero

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11
Q

Define force constant

A

The force per unit extension.

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12
Q

Why does the acceleration of the trolley decrease…

A

the resultant force is smaller.

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13
Q

Centre of gravity

A

A point where the entire weight of the object appears to act.

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14
Q

Moment of a force

A

force x perpendicular distance from line of force

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15
Q

State two conditions necessary for the rod to be in equilibrium. (moments)

A
  • Net force=0

- Net moment=0 (clockwise moments= anticlockwise moments)

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16
Q

1 Watt

A

1 joule of energy transferred per 1 second.

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17
Q

Similarity of distance and displacement

A

Both measured in metres

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18
Q

Difference between distance and displacement

A

One is scalar, one is a vector

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19
Q

The gradient of a velocity-time graph..

A

…is acceleration

20
Q

In an experiment of free fall, explain why g may be less then 9.81

A
  • reaction time of student

- displacement isn’t precise enough

21
Q

Sky diver jumps- immediately after jumping…

A
  • Only force is the weight/drag = 0
  • net force = weight
  • acceleration = g/9.8(1 m s-2)
22
Q

Sky diver before terminal velocity…

A
  • Drag increases (with speed)
  • drag prop. speed^2
  • Net or resultant or total force decreases
  • weight > drag
  • Acceleration is less than g
23
Q

Sky diver at terminal velocity….

A
  • weight = drag
  • net force = 0
  • acceleration = 0
  • constant speed or velocity
24
Q

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.

A

Transformed to heat/thermal (energy)

25
Q

Define work done.

A

force x distance moved in the direction of the force

26
Q

Define Power.

A

The amount of energy transformed from one form to another per second. (P= work done/time)

27
Q

Explain why the effciency of mechanical device can never be 100%

A

energy is always lost as heat.

28
Q

Principle of moments

A 
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)
29
Q

State and how explain how the pressure would change, if the same screw was secured much closer to the pivot.

A
  • Pressure is greater

- because the force/F is larger (to provide the same moment)

30
Q

Define the ultimate tensile strength of a material.

A

Maximum stress material can withstand (before fracture)

31
Q

State Hooke’s Law.

A

extension (or compression) is proportional to force (as long as elastic limit is not exceeded)
-F=kx

32
Q

State the main characteristics of rubber (stress-strain graph)

A
  • 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
33
Q

Define velocity

A

velocity = rate of change of displacement

34
Q

State the physical properties of a brittle metal (stress-strain graph).

A
  • The material is brittle.
  • The material is also elastic.
  • No plastic deformation.
35
Q

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.

A
  • 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)
36
Q

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.

A
  • 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)
37
Q

A crate is pushed along a rough horizontal surface at a constant speed. State what happens to the work done on the crate.

A

(Work done against friction generates) heat / thermal energy / internal energy

38
Q

The vertical upward force on the spaceship stays constant. Explain why the acceleration of the spaceship increases after lift off.

A

The mass/weight (of spaceship) decreases as it loses fuel.

39
Q

Area under a force-extension graph…

A

…Elastic Potential Energy

40
Q

Two factors that affect the magnitude of drag force acting on object falling through air.

A
  • The surface area
  • Velocity
  • ‘Aerodynamic” shape
41
Q

Explain what is meant by gravitational potential energy without using an equation.

A

GPE linked to ‘position’ / height (in a gravitational field)

42
Q

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.

A

-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

43
Q

The acceleration of an electron decreases as its velocity increases. Why?

A 
The mass (of the electron) increases
as its speed approaches the speed of light
44
Q

Describe one example where elastic potential energy is stored.

A

stretched elastic band

45
Q

Work done stretching a spring equation(s)…

A

1/2x F x (x)

or

1/2 x k x (x)^2

46
Q

Pressure units

A

kg m^-1 s^-2

47
Q

Power units

A

kg m^2 s^-3

Best Physics (9 decks)

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