Physics 1 - Work, Energy and Power

Question 1

1.2P List the units and unit symbols for: moments

Answer 1

Newton Metre (Nm)

Question 2

1.2P List the units and unit symbols for: momentum

Answer 2

Kilogram metre per second (kg m/s)

Question 3

1.3 Plot a distance-time graph for the following motion: stationary, constant speed, acceleration, deceleration

Answer 3

SEE ONENOTE
Stationary - horizontal line
Constant speed - straight line
Acceleration - gradient increasing
Deceleration - gradient decreasing

Question 4

1.3 Describe how speed can be determined from a distance-time graph

Answer 4

Find the gradient

Question 5

Average speed

Answer 5

Change in distance/change in time

Question 6

1.4 Write down another equation for average speed if acceleration is constant in words and symbols

Answer 6

average speed=1/2(initial speed+final speed)

Question 7

1.5 Practical: Describe a generic experiment to determine the average speed of an object

Answer 7

Get a set distance and measure it (ruler, tape measure, trundle wheel)
State how you will measure the time (stopwatch, light gates etc)
State the method (self explanatory)
Repeat, remove anomalies and take an average
Calculate the average speed

Question 8

1.7 Plot a velocity-time graph for the following motion: stationary, constant speed, acceleration, deceleration

Answer 8

Stationary - Horizontal line on zero
Constant speed - horizontal line
Acceleration - Straight diagonal line going upwards
Deceleration - Straight diagonal line going downwards

Question 9

1.8 Describe how acceleration can be determined from a velocity-time graph

Answer 9

Calculate the gradient

Question 10

1.9 Describe how distance/displacement travelled can be determined from a velocity-time graph

Answer 10

Calculate the area from the x axis to the line.

Above the axis is a positive displacement, vice versa.

Question 11

1.10 Write down the equation relating final speed, initial speed, acceleration and distance moved in words and symbols

Answer 11

Final speed squared = initial speed squared + (2 x acceleration x distance)
v^2 = u^2 + 2as

Question 12

1.11 Describe the possible effects of forces between bodies

Answer 12

Change speed, shape or direction

Question 13

1.13 State how a vector quantity is different from a scalar quantity

Answer 13

A scalar has only magnitude, a vector has magnitude and direction

Question 14

1.15 Describe how to calculate the resultant force of several forces acting along a line

Answer 14

Choose one direction to be positive and the other negative. Add the quantities together using the signs used

Question 15

Is force a scalar or vector?

Answer 15

Vector

Question 16

1.16 Define friction

Answer 16

A force that opposes motion

Question 17

1.17 Write down the relationship between unbalanced forces, mass and acceleration in words and symbols

Answer 17

Resultant force = mass x acceleration

∑F=ma

Question 18

1.19 Define the thinking distance and braking distance

Answer 18

Thinking distance: distance travelled between spotting the hazard and pressing the brakes

Braking distance: distance travelled between pressing the break and coming to a complete stop

Question 19

1.19 Define stopping distance

Answer 19

Thinking distance + braking distance

Question 20

1.20 Describe and explain the factors that affect thinking distance

Answer 20

Speed - travel further in the same amount of time

Reaction time - affected by alcohol, tiredness, distraction from phone

Question 21

1.20 Describe and explain the factors that affect braking distance

Answer 21

Mass - increases momentum and KE
Road/car conditions - reduces braking force
Speed - has greater kinetic energy so takes longer to come to a complete stop

Question 22

1.21 Describe and sketch the forces acting on a falling object

Answer 22

Weight - downwards

Drag/air resistance/friction - upwards (smaller)

Question 23

1.21 Define terminal velocity and sketch a diagram

Answer 23

Forces reach equilibrium - drag = weight

Therefore the object travels at a constant speed

Question 24

1. 22 Practical: Design an experiment to investigate how extension varies with applied force for
   a. Helical springs
   b. Metal wire
   c. Rubber band

Answer 24

Set up a clamp, attached to the table by another clamp, with a ruler set upnext to a spring.

Measure the initial length of the spring, then add different masses (IV) and measure the extension (DV)

Accuracy - make sure the ruler is close to avoid a parallax error. Repeat the experiment and calculate an average extension

Plot a force extension graph; put a straight line through it - the gradient is the spring constant.

Wire: do the same but use a micrometre
Rubber band: measure the extension as masses are removed to show the hysteresis in the graph

Question 25

1.23 Sketch a force-extension graph for a helical spring, metal wire and rubber band and label Hooke’s law region, elastic behaviour, plastic behaviour

Answer 25

Linear part = Hooke’s law region, elastic behaviour

Non linear = plastic behaviour

Question 26

1.23 State Hooke’s law, and put as an equation

Answer 26

The extension of the material is proportional to the force applied

Force = k (spring constant) x (extension)

Question 27

1.24 Describe elastic behaviour

Answer 27

The ability to recover its original shape after forces of deformation have been removed

Question 28

1.25P Write down the relationship between momentum, mass and velocity in words and symbols

Answer 28

Momentum = mass x velocity
p = mv

Question 29

1.27P State the law of conservation of momentum

Answer 29

The total momentum before a collision = total momentum after a collision

Question 30

1. 27P Write down the momentum equation for
   a. Two objects colliding and separating
   b. Two objects colliding and sticking
   c. Two objects separating due to an explosion

Answer 30

m_1 u_1+m_2 u_2=m_1 v_1+m_2 v_2
m_1 u_1+m_2 u_2=(m_1+m_2)v
0=m_1 v_1+m_2 v_2

Question 31

1.28P Write down the equation for resultant force (impulse) in terms of momentum and time taken in words and symbols

Answer 31

Resultant net force = change in momentum/time taken
∑F=(mv−mu)/t
F=Δp/t

Question 32

1.26P Describe and explain how safety features work during a collision using the idea of momentum

Answer 32

Change in momentum remains the same but increasing the time taken reduces the impulse (net force).

Seat belt, crumple zones and airbags all increase the time over which there is a change in momentum (F = Δp/t)

Question 33

1.29P Write down Newton’s 3rd law

Answer 33

If Object A applies a force on Object B, B applies a force on A that is:

Equal in magnitude
Opposite in direction
Same fundamental force
Along the same line

Question 34

1.30P Write down the relationship between the moment of a force, force and perpendicular distance from a pivot in words and symbols

Answer 34

the turning moment of a force=force×perpendicular distance to pivot
M=F×d

Question 35

1.31P State where the weight of an object, such as a rod, can be considered to act from

Answer 35

The centre of gravity of the object

Question 36

1.32P State the principle of moments

Answer 36

When an object is in equilibrium, the sum of the clockwise moments is equal to the sum of the anti-clockwise moments

Question 37

1.32P Describe how to use the principle of moments with several parallel forces acting on an object

Answer 37

Calculate the clockwise moments
Calculate the anti-clockwise moments
clockwise moments=anti−clockwise moments
Remember also that the vertical and horizontal forces are also balanced, therefore
force to the left=forces to the right
upwards forces=downwards forces

Question 38

1.33P Describe how the upwards force generated by two pivots supporting a beam is affected by the position of a heavy object placed on the beam

Answer 38

The support closest to the mass provides the greater upwards force

As the object moves to the other one, the force decreases for the closer one and increases for the one the object’s getting closer to