Question

The specific heat capacity of water= 4200 J kg-1K-1
1) How much heat energy is required to warm a) 1 kg of water from 14°C to 15°C; b) 5 kg of water from 14°C to 15°C; and c) 5 kg of water from 14°C to 22°C. THANK YOU!!

Answer 1

\[J kg ^{-1} K ^{-1}\] this is the correct way of writing the unit

Answer 2

Use the formul heat required =\(mc \Delta t\)

Answer 3

q=McDelta T

Answer 4

where m is mass c is specific heat capacity ,delta t=change in temperature

Answer 5

ok thanks

Answer 6

yw :)

Answer 7

i worked it out...is the answer 4200J

Answer 8

a b or c?

Answer 9

for a)

Answer 10

right !

Answer 11

hmm and b) is 21000J while c) is 1.68*10\[1.68\times10^{5}\] am i right???

Answer 12

yep :)

Answer 13

was it that simple?

Answer 14

question 2!
one way to measure the energy contained in a beam of x-rays is to absorb the beam by a piece of pure graphite. If x-rays are shone on to a cavity in a block of graphite of mass 10 g (0.01 kg), and a rise in temperature of 0.005K, work out the energy supplied by the beam.

Answer 15

oh and the specific heat capacity of graphite is 600\[J kg ^{-1}K ^{-1}\]

Answer 16

same formula !

Answer 17

ok......just making sure.
question 3!
An electric drill consuming energy at a rate of 200 W is used to make a small hole in a block of copper of mass 2 kg. Assuming that 80% of the electrical energy used ends up in the block as heat, and that this heat is spread evenly throughout the block, estimate its rise in temperature in 10 seconds.

Answer 18

Why dont you make a new question? rather than lump several into one post?

Answer 19

ok @kym02 i'll give a brief info.

so energy is 200 W i.e. it uses 200 J in 1 second, correct?

Answer 20

um i honestly dont know....im a beginner. Dont really know about this stuff! sorry!

Answer 21

Ok, then there is one concept.

W means Watt. Watt is the unit of power of a machine.

We say that the power of a machine is the amount of work it can do in 1 second.(i.e. rate of doing work,)

Hence its unit is Watt(W) also expressed as Joule/second.

so 200 W basically means that the machine will use 200 Joules of energy in 1 second.

Ok?

Answer 22

ok i understand.

Answer 23

Fine. so if the machine uses 200 Joules of energy in 1 second, how much of energy would it use in 10 seconds?

Answer 24

2000 J.

Answer 25

Ok. 2000 J is the electrical energy used.

Now he says that 80% of this 2000 J is used as heat energy.

So what is 80% of 2000 ?

Answer 26

1600

Answer 27

Thats right.

So this 1600 is the heat energy.

As shown above, Heat energy = Mass x sp. heat capacity x rise in temp.

You have mass = 2 kg, sp. heat capacity(c) = 400 JKg^-1K^-1, can you find the rise in temperature?

Answer 28

i dont know that one, do i have to transpose?

Answer 29

Yep you have to. above there was a formula mentioned

Heat energy = m x c x delta T
Here Heat energy = 1600, m = 2 kg, c = 400 J/KgK, u need to find delta T

Answer 30

m means Mass; c means specific heat capacity and delta T means the rise in temperature.

Answer 31

\[E _{H}=mcΔT\]
so the temperature rise will be:
EH divided by mass times c
am i right?

Answer 32

Thats perfectly correct. Just type d ans also when you find it. :)

Answer 33

ok i will, im working on it

Answer 34

Is the answer 2°C?

Answer 35

Yes. :)

Answer 36

yes!!!!! thanks :) i have one more question though

Answer 37

a)How much potential energy does a 2.0 kg lump of copper possess when it is lifted 3.0 m from the ground? (Take g to be 10 N kg^-1.)
b) If it is dropped, how much kinetic energy will it have just before it hits the ground?
c) If all that energy is converted to heat, and if all that heat goes into the copper, what rise in temperature would you expect?

That's all ! :)

Answer 38

a) m = 2, h = 3, g = 10. Use Potential Energy = mgh.

b) Potential Energy found in a) = Kinetic Energy
(By law of conservation of energy)

c) Whatever PE you get, assume that as heat energy, the use C , M of copper to find rise in temp by formula EH = m.c. delta T.

Answer 39

whats the unit for a) ???

Answer 40

a) Any form of energy, whether potential energy, electric energy, heat energy, is expressed in joules( J ) (Please please note this fact; )

Answer 41

ok ok so a) =60 J

Answer 42

Thats correct.

Answer 43

and c) = \[7.5\times 10^{-2} \deg C\]

Answer 44

Which is correct, :)

Answer 45

I hope you're familiar with law of conservation of energy right?

Answer 46

no but i will just look back in a textbook! thank you soooo much!!! you saved me!! :)

Answer 47

yeah no probs as long as you're familiar with concepts and numericals :)