4.17 Answers

4.17 Answers

07 September 2011

14:45

ADs and DISADs of ENERGY SOURCES-answers.docx Download this file

Starter for 4.16

 Starter for 4.16

DragnDropEnergy.swf Download this file

Entrance Activity

Tell the person next to you...

Starter.ppt Download this file

4.15

·         

4.15 use the relationship between power, work done (energy transferred) and time taken:

          power = work done            P = Wd

                       time taken                    t

P = Wd / t

P = E / t

P = Power (Watts, W)

Wd = Work Done (Joules, J)

E = Energy Transferred (Joules, J)

t = Time (s)

4.14 Entrance Activity Answers

Tell the person next to you...

·         You can run up the stairs in the Science block in 30 seconds.

·         Mr. Roff can run up the stairs in the Science block in 20 seconds.

·         Who is the most powerful?  Why?

·         Mr Roff.  He does more work running up the stairs (because has a higher weight) in a shorted time so he is more powerful

 

·         It takes 2 minutes to fill the 20 litre sinks in this room with water. 

·         How fast is the sink filling?

·         10 litres/min

·         At what rate is the sink filling?

·         10 litres/min

·         How long would it take to fill a 10 litre sink?

·         1 min

Power Questions

PFY p.120

f) Power is the rate of doing work
Power (in Watts) = work done (in joules) / time (in seconds)

g) 1 watt is a rate of working of one joule per second

13) A girl does 1000 joules of work in 5 seconds. What power does she develop?
P = Wd/t
P = 1000/5
P = 200 W

14) A man lifts a weight of 300N through a vertical height of 2 m in 6 seconds. What power does he develop?
Wd = F x d
Wd = 300 x 2
Wd = 600J

P = Wd/t
P = 600/6
P = 100 W

16) A crane lifts a load of 3000N through a vertical height of 10 m in 4 seconds. What is its rate of working ina) Watts
Wd = F x d
Wd = 3000 x 10
Wd = 30,000J

P = Wd/t
P = 30,000 / 4
P = 7,500 W

b) Kilowatts
7,500 / 1000 = 7.5 kW

4.13

·         

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

<<CoE.ppt>>

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CoE.ppt Download this file