CoE questions

PFY p.121

19 

a) W = m x g       50 x 10 = 500 newtons

b) GPE= m x g x h     50 x 10 x 4 = 2000 joules

c) GPE = KE      2000 joules

Collins, p.91

Q3

a) GPE= m x g x h      GPE = 35 x 10 x 30      GPE= 10500 joules

b) KE = 1/2 mv^2    10500 = 1/2 x 35 x v^2      V= 24.5m/s

c) There is energy lost due to friction as heat.

4.13

·         

4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work

CoE.ppt Download this file

4.12

4.12 recall and use the relationship:

                 kinetic energy = ½ × mass × speed²

                                 KE = ½ × m × v²

KE formula.ppt Download this file

4.11

·         

4.11 recall and use the relationship:

   gravitational potential energy = mass × g × height

                              GPE = m × g × h

GPE formula.ppt Download this file

4B2 highest to lowest GPE.swf Download this file

4B2 GPE calculation of car moving downhill.swf Download this file

4.10

·         

4.10 understand that work done is equal to energy transferred

PFY p.112

1. 

a) The work done (measured in joules) is equal to the force (in newtons) multiplied by the distanced moved (in metres)

b) 1 joule is the work done when a force of one newton moves through a distance of one metre (in the direction of the force)

d) work done= energy transferred 

work done = force x distance.

work done = 5 newtons x 2 metres.

                  = 10J 

work done = force x distance

work done = 500 newtons x 40 metres.

                  = 20KJ or 20000J 

Collins p. 91

work done = force x distance

work done = 50000/4000

                  = 12.5m

4.9

·         

4.9 recall and use the relationship between work, force and distance moved in the direction of the force:

       work done = force × distance moved         

Wd = F × d

	<<Work formula.ppt>>
			<<4B1 work done pushing a wheelbarrow.swf>>		<<4B1 work done skiing downhill.swf>>

Work formula.ppt Download this file

4B1 work done skiing downhill.swf Download this file

4B1 work done pushing a wheelbarrow.swf Download this file

Starter - answers

Tell the person next to you...

·         Imagine pushing a king sized bed from one side of the classroom to the other

·         Would it make you feel tired? 

o    Yup!

·         Would you have to work hard to push it?

o    Yup!

·         What could you change so you have to do less work pushing?

o    Anything that decreases the force needed (reduce friction by putting wheels on it, ice under it, etc)

o    Anything that decreases the distance travelled (only push it half way!, etc)

o    So the formula for work must contain force and distance