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Broadoak School GCSE Physics

Energy & Motion  Calculations Practice

- This file contains questions for you to practice on - it assumes that you already have been taught
     about how to do them.
- The computer won't keep score.
- You shouldn't need a calculator, but it may help to write down your working rather than try to do
     it all in your head. You ought to write out your working anyway, because it's often worth marks!

Contents

   - Click on these headings :.

Work, Force & Distance

Power, Work & Time

Pressure, Force & Area

Acceleration and Force                                                  (Higher paper only)

Kinetic Energy  and Gravitational Potential Energy       (Higher paper only)

Click on "File", "Exit" to finish.


No - try again


Yes


work
Work, Force & Distance

"Work" is the name we give to energy that's used to move something.
We also call it "mechanical work done". Being energy, we measure it in Joules.

QUESTION 1
     If I push a book 2 metres along a desk with a force of 2 Newtons, how much energy will it take?

1 Joule

2 Joules

4 Joules

QUESTION 2
     If you pushed a wardrobe across the floor with a force of 200 Newtons, and you
     did 400 Joules of work, how far did you push it?

2 metres

8 metres

80000 metres

QUESTION 3
     An  beaver drags a fallen branch for 15 metres through a forest to the edge of its dam, and
     needs to pull with a force of 30 Newtons. How much work did it do?

2 Joules

450 Newtons

450 Joules

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Yes

Work = Force x Distance
          = 2 x 2
          = 4 Joules


No

80,000 metres ? That's rather a long way!

Look at the "triangle" in the diagram.
If Work = force times distance, then distance = work divided by force.
So try 400 DIVIDED BY 200.


No

Work is measured in Joules


Power

Power is the RATE of doing work (remember that "work" means energy).

QUESTION 1
          A clockwork train is wound up, storing 300 Joules of energy in the spring.
          When the train is released, it runs for 30 seconds.
          What is the power developed by the train?

9,000 Watts

300 Joules

10 Watts

QUESTION 2
          Another clockwork train develops 15 Watts of power for 20 seconds.
          How much energy is stored in this train's spring?

0.75 Joules

300 Joules

300 Watts

QUESTION 3
          If a device stores 500 Joules of energy, and develops a power of 50 Watts, how
          many seconds will it run for?

25,000 seconds

500 seconds

10 seconds

QUESTION 4
          Another device takes in 1200 Joules of energy in 2 minutes. What is its power?

2400 Watts

600 Watts

10 Watts

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Pressure

We work out pressure using :

Remember that a small force can create a large pressure if the area is small.

QUESTION 1
          A stone pillar exerts a force of 10,000 Newtons on the ground.
          If the base of the pillar is 2 square metres, what is the pressure on the ground?

5,000 Newtons

5,000 Pascals

20,000 Pascals

QUESTION 2
          My weight is 750 Newtons, and the total area of the soles of my shoes is 0.05 square metres.
          What pressure do I exert on the ground?

750 / 0.05 = 15,000 Pa

750 x 0.05 = 37.5 Pa

QUESTION 3
          A small boy pokes a stranded jellyfish with a stick. He pokes it with a force of 10 Newtons,
          and the end of the stick has an area of 1 square centimetre.
          If it takes a pressure of 150,000 Pa to puncture the skin of the jellyfish, does the stick
          go in?

Yes

No

QUESTION 4
         The atmosphere exerts a pressure of 100,000 Pa.
         What force does it exert on 1.5 square metres?

150,000 Newtons

100,000 Pa

150,000 Pa

QUESTION 5
          The diagram shows a hydraulic
           jack used to lift cars in a garage

          Remember that the pressure is the same at all points in the liquid, which means
          that    Force/Area at one piston = Force/Area at the other.

          What is the pressure in the liquid?

3,000 Pa

30,000 Pa

300,000 Pa

                         The pressure in the liquid exerts a force on the large piston which lifts the car.
                         What is this force?

15,000 N

150,000 N

1,500,000 N

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acceleration
Acceleration and Force

Higher paper only

There are two equations to remember :

         Where    a  is acceleration   (in m/s/s)                   F  is force          (in Newtons)
                       v  is final velocity   (in m/s)                     m  is mass          (in kg)
                       u  is initial velocity  (in m/s)                     a  is acceleration (in m/s/s)
                       t  is time                (in seconds)

QUESTION 1
     A motorbike travelling at 3 m/s accelerates to 11 m/s over a period of 4 seconds.
     What is its acceleration?

2 metres per second

2 metres per second per second

3 metres per second per second

QUESTION 2
      A rocket decelerates at 5 m/s/s from 30 m/s to 10 m/s.
      How long does it take to do this?

4 seconds

40 seconds

0.2 seconds

QUESTION 3
      An ice skater of mass 70 kg is pushed, and accelerates at 2 m/s/s.
      What was the force of the push?

35 Newtons

70 Newtons

140 Newtons

QUESTION 4
      Another ice skater, of mass 60 kg, is pushed with a force of 30 Newtons.
      What is her acceleration?

0.5 m/s/s

2 m/s/s

180 m/s/s

1800 m/s/s

QUESTION 5
      A Year 10 pupil fires a stone of mass 50 g from a catapult towards an unsuspecting
      physics teacher. If the average force from the catapult on the stone is 5 Newtons, what
      is the acceleration of the stone?

10 m/s/s

100 m/s/s

25 m/s/s

                      So if that catapult accelerated the stone for 0.2 seconds, how fast would the
                      stone be travelling as it left the catapult?

20 m/s

200 m/s

100 m/s

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kineticandpotential
Kinetic Energy and Gravitational Potential Energy

Higher paper only

The equations are :

Where: m  is mass     (in kg)
            v  is velocity  (in m/s)
            h  is height     (in metres)
            g  is the Earth's gravitational
                pull  (=10 Netwons per kg)

Remember that if you throw a ball upwards with a kinetic energy of say, 20 Joules, it will rise up until it has converted all of that 20 Joules into potential energy (and has no more kinetic energy - i.e. it stops for a moment at the top of its flight).
If you drop a ball so that it loses 20 Joules of potential energy, it will have 20 Joules of kinetic energy at the bottom.
                           Just remember that the energy has to GO somewhere!

QUESTION 1
          A hungry cat of mass 2 kg rushes towards its dinner at 3 m/s. What is its kinetic energy?

6 Joules

18 Joules

9 Joules

QUESTION 2
          Meanwhile, an observant mouse decides not to become the cat's dessert, and heads
          for the horizon also at a velocity of 3 m/s.
          If the mouse has a mass of 200 g, what is its kinetic energy?

600 Joules

0.9 Joules

1800 Joules

QUESTION 3
          A small boy throws a 0.5 kg ball to his friend, who is perched 3.2 metres up in a tree.
          How much potential energy does the ball gain?

16 Joules

1.6 Joules

9 Joules

How much kinetic energy did the boy give the ball when he threw it up there?

32 Joules

16 Joules

The boy up the tree then drops the ball.
How much kinetic energy will it have when it hits the first boy on the head?

32 Joules

16 Joules

How fast will the ball be travelling when it hits him?

8 m/s

16 m/s

64 m/s

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No

Acceleration is measured in Metres per Second per Second (m/s/s)


Yes


Yes


Yes

F = m x a
   = 70 x 2
   = 140 Newtons


Yes

F = ma    means that   a = F/m
                                     = 30/60
                                     = 0.5 m/s/s


No

F = ma      means that   a = F/m.
             You've just got it upside down. Try again.


No

F = ma   means that  a = F/m
              You've just multiplied them
              (and incidentally got a result that would kill the ice skater!)


Yes

acceleration = F/m
                   = 5/0.05    (remember it's got to be kilogrammes!)
                   = 100 m/s/s   (quite a savage acceleration!)


Yes


No

Power = energy DIVIDED BY time.
You've multiplied them together.


No

Power is measured in WATTS.


Yes

Power = energy divided by time
           = 300 divided by  30
           = 10 Watts


No

Power = Energy divided by Time.
This means that   Energy = Power TIMES Time.
You've divided them - try again


Yes

Energy = Power x Time
            = 15 x 20
            = 300 Joules

Notice that this is the same ENERGY as the
last question - but the train was more powerful
so it didn't last as long.


No

Energy is measured in JOULES.


Yes

Power = Energy divided by Time.
This means that Time = Energy divided by Power
                                = 500 divided by 50
                                = 10 seconds


No

Power = Energy DIVIDED BY Time


Almost!

Remember that the time must be in SECONDS.


Yes

First, get the time into SECONDS : 2 minutes  = 120 seconds

Power = Energy divided by time
           = 1200 divided by 120
           = 10 Watts


No

You've missed out the "half", and
forgotten to "square" the velocity.


Almost!

You've just forgotten the "half".


Yes


No

You've forgotten the "half", and also the "squared".
You've also forgotten that the mass must be in kg.


Yes


Yes

Potential energy = m x g x h
                         = 0.5 x 10 x 3.2
                         = 16 Joules


Almost!

You've just forgotten to multiply by "g"
(Remember that g = 10 N/kg)


Yes

The same as the potential energy - because
that's where the potential energy came from.


Yes


Almost!

You've done the right things - but
forgotten to square-root the answer.


No

Pressure is measured in PASCALS
(Remember that a Pascal (Pa) is the
   same as a Newton per square metre.)


Yes


No

You need to DIVIDE, not multiply.


Correct


No

You're working out a FORCE,
and forces are in NEWTONS.


Yes

Force = pressure x area
          = 100,000 x 1.5
          = 150,000 Newtons.

YOU have a surface area of around 1.5 square metres.
This means that the atmosphere is exerting 150,000 N
on you right now - that's about the same as the weight
of ten cars ! Honest!


Yes


Yes

So the system has made the force BIGGER,
in the same sort of way that we can use a lever
to make a force bigger.