AQA GCSE Physics 23 Work, Energy

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AQA GCSE Physics 2-3Work, Energy Momentum

• GCSE Physics pages 146 to 159

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AQA GCSE Specification

• WORK ENERGY
• 12.3 What happens to the movement energy when
• things speed up or slow down?
• Using skills, knowledge and understanding of how
  science works
• to discuss the transformation of kinetic
  energy to other forms of energy in particular
  situations.
• Skills, knowledge and understanding of how
  science works set in the context of
• When a force causes a body to move through a
  distance, energy is transferred and work is done.
• Work done energy transferred.
• The amount of work done, force and distance
  are related by the equation
• work done force applied distance moved in
  direction of force
• Work done against frictional forces is mainly
  transformed into heat.
• Elastic potential is the energy stored in an
  object when work is done on the object to change
  its shape.
• The kinetic energy of a body depends on its
  mass and its speed.
• HT Calculate the kinetic energy of a body using
  the equation
• kinetic energy ½ mass speed2

• MOMENTUM
• 12.4 What is momentum?
• Using skills, knowledge and understanding of how
  science works
• to use the conservation of momentum (in one
  dimension) to calculate the mass, velocity or
  momentum of a body involved in a collision or
  explosion
• to use the ideas of momentum to explain safety
  features.
• Skills, knowledge and understanding of how
  science works set in the context of
• Momentum, mass and velocity are related by the
  equation
• momentum mass velocity
• Momentum has both magnitude and direction.
• When a force acts on a body that is moving, or
  able to move, a change in momentum occurs.
• Momentum is conserved in any
  collision/explosion provided no external forces
  act on the colliding/exploding bodies.
• HT Force, change in momentum and time taken for
  the change are related by the equation
• force change in momentum / time taken for the
  change

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Energy and workNotes questions from pages 146
147

• What is meant by work?
• Copy both of the equations for work on page 146
  along with the units used.
• Copy and answer questions (a) and (b) on pages
  146 and 147.
• Explain two ways in which the force of friction
  causes energy to be transformed into heat.
• Copy the Key Points on page 147.
• Answer the summary questions on page 147.

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Energy and work ANSWERS

• In text questions
• To the surroundings as heat energy and sound
  energy
• 300 J

• Summary questions
• (a) 96 J
• (b) 96 J
• (a) (i) 90 J
• (ii) 4500 J
• (b) 0.60 m

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Kinetic energyNotes questions from pages 148
149

• How can gravitational potential energy be
  calculated? (see the practical on page 148)
• Copy the equation for kinetic energy at the top
  of page 149 along with the units used.
• Repeat the calculation below the kinetic energy
  equation but this time with a mass of 400 kg
  moving at a speed of 8 m/s.
• What does elastic mean?
• What is elastic potential energy?
• Copy and answer question (b) on page 149.
• Copy the Key Points on page 149.
• Answer the summary questions on page 149.

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Kinetic energy ANSWERS

• In text question
• (b) Heat energy transferred to the surroundings,
  the foot and the shoe also sound energy.

• Summary questions
• 1. (a) (i) Chemical energy from the loader is
  transferred into elastic potential energy of the
  catapult and some is wasted as heat energy.
• (ii) Elastic potential energy in the catapult
  is transformed into kinetic energy of the object
  and the rubber band and heat energy (plus a
  little sound energy).
• (b) (i) 10 J
• (ii) 10 J
• 2. (a) 3800 N
• (b) Friction due to the brakes transforms it
  from kinetic energy of the car to heat energy in
  the brakes.
• (c) 800 kg

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MomentumNotes questions from pages 150 151

• What is momentum?
• Copy out the equation at the top of page 150.
  State the units for each quantity in the
  equation.
• Copy and answer question (a) on page 150.
• Under a heading Conservation of momentum copy
  out the statement in bold at the bottom of page
  150.
• Copy out the worked example on page 151.
• Copy and answer question (b) on page 151.
• Copy the Key Points on page 151.
• Answer the summary questions on page 151.

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Momentum ANSWERS

• In text questions
• 240 kg m/s
• 0.48 m/s

• Summary questions
• (a) mass, velocity
• (b) momentum, force
• 2. (a) 5000 kg m/s
• (b) velocity
• momentum / mass
• 5000 / 2500
• 2.0 m/s

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More on collisions and explosionsNotes questions
from pages 152 153

• Apart from size what other property does momentum
  have?
• Copy and answer question (a) on page 152.
• Explain how conservation of momentum applies in
  an explosion.
• Why do guns recoil?
• Copy and answer question (b) on page 153.
• Copy the Key Points on page 153.
• Answer the summary questions on page 153.

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More on collisions and explosions ANSWERS

• In text questions
• The boat and the person who jumps off move away
  with equal and opposite amounts of momentum.
• 25 m/s

• Summary questions
• (a) momentum
• (b) velocity
• (c) force
• (a) 60 kg m/s
• (b) 1.5 m/s

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Changing momentumNotes questions from pages 154
155

• What is the purpose of a cars crumple zones?
• Copy the key points on page 155.
• Copy and answer questions (a), (b) and (c) on
  pages 154 and 155.
• Copy the Key Points on page 155.
• Answer the summary questions on page 155.

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Changing momentum ANSWERS

• In text questions
• If a child falls off a swing, the rubber mat
  reduces the impact force by increasing the impact
  time when the child hits the ground.
• The force is bigger
• 1800 N

• Summary questions
• (a) stays the same
• (b) increases
• (c) decreases
• 2. (a) 24 000 kg m/s
• (b) (i) 2000 N
• (ii) 800 N

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Forces for safety Notes questions from pages 156
157

• Answer questions 1 and 2 on pages 156 and 157.

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Forces for safety ANSWERS

• The air bag increases the time taken to stop the
  person it acts on. This reduces the force of the
  impact. Also, the force is spread out across the
  chest by the air bag so its effect is lessened
  again.
• (a) 26 100 kg m/s
• (b) 34.8 m/s
• (c) Yes.

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How Science Works ANSWERS

• No. The upright position is slightly greater
  although there is no significant difference
  between the three sets of readings.
• The upright position propels the ball further.
  This prediction is even stronger if the 2nd
  go/front measurement is considered to be an
  anomaly.
• No. The measurements have a wide range within
  each set. There is even overlap of results.
• Position of the releae point.
• Categoric.
• By measuring the angle of the spoon to the
  upright.
• More information can be obtained. A graph can
  also be drawn and a pattern discerned (or not).