# can someone pls explain what these symbols stand forWatch

#1
in the work done equation i understand up to fxab and then im completely lost if someone could explain it out it would be greatly appreciated

http://gyazo.com/da63568a72336831fe6d14304c11331b
0
4 years ago
#2
(Original post by pappu)
in the work done equation i understand up to fxab and then im completely lost if someone could explain it out it would be greatly appreciated
you really need to post the question ?
0
4 years ago
#3
It says above that Work Done = Force x Distance, where distance is from A to B

Pressure (p) = Force (F) / cross sectional area (A), therefore F=pA

I'm not too sure what's happening with the pA(V/A) bit, but if you've been given the mass flow rate 'm' then you know that m=ρAV, so rearranging gives V=m/(ρA)

The next part shows that Work done = pA(m/ρA) but then the A that I highlighted previously seems redundant? Somebody let me know if I missed something there.

But now the cross sectional areas can cancel out to give Work Done = pm/ρ

EDIT: Actually I'm still wondering how they got Velocity/Cross sectional area from Distance :/

EDIT 2: If 'm' is actually for Mass let me know that as well, although it wouldn't really make sense for it not to
1
4 years ago
#4
(Original post by pappu)
in the work done equation i understand up to fxab and then im completely lost if someone could explain it out it would be greatly appreciated

http://gyazo.com/da63568a72336831fe6d14304c11331b
1. W = F.AB (you understand this bit so far, it is just work = force.displacement)

Now, given that Pressure = Force/Area, then F = pA. Therefore,

2. W = pA.(AB)

Now the distance (AB) is given by (volume of AB)/(cross-sectional area of AB). That is (AB) = V/A. [Just think area*distance = volume and re-arrange]. Therefore,

3. W = pAV/A (obviously the A's will cancel, which they will do later)

Now density = mass/volume, or we can say volume = m/density. We will represent density by the letter (rho), which looks like a p. Therefore, V = m/(rho). Subbing into 3 we arrive at:

4. W = pAm/(A(rho))

We will now cancel out the A's to obtain:

5. W = pm/(rho)

This has brought us to the end of their first line. Check you understand it so far.

Next they define "specific work" to be work/mass (like specific heat capacity is heat capacity/mass).

Specific work = W/m = pm/(m(rho)) = p/(rho)
1
4 years ago
#5
(Original post by Ruthless Dutchman)
It says above that Work Done = Force x Distance, where distance is from A to B

Pressure (p) = Force (F) / cross sectional area (A), therefore F=pA

I'm not too sure what's happening with the pA(V/A) bit, but if you've been given the mass flow rate 'm' then you know that m=ρAV, so rearranging gives V=m/(ρA)

The next part shows that Work done = pA(m/ρA) but then the A that I highlighted previously seems redundant? Somebody let me know if I missed something there.

But now the cross sectional areas can cancel out to give Work Done = pm/ρ

EDIT: Actually I'm still wondering how they got Velocity/Cross sectional area from Distance :/

EDIT 2: If 'm' is actually for Mass let me know that as well, although it wouldn't really make sense for it not to
Their V actually represents volume. See my answer above for full working.
0
#6
(Original post by Doctor_Einstein)
1. W = F.AB (you understand this bit so far, it is just work = force.displacement)

Now, given that Pressure = Force/Area, then F = pA. Therefore,

2. W = pA.(AB)

Now the distance (AB) is given by (volume of AB)/(cross-sectional area of AB). That is (AB) = V/A. [Just think area*distance = volume and re-arrange]. Therefore,

3. W = pAV/A (obviously the A's will cancel, which they will do later)

Now density = mass/volume, or we can say volume = m/density. We will represent density by the letter (rho), which looks like a p. Therefore, V = m/(rho). Subbing into 3 we arrive at:

4. W = pAm/(A(rho))

We will now cancel out the A's to obtain:

5. W = pm/(rho)

This has brought us to the end of their first line. Check you understand it so far.

Next they define "specific work" to be work/mass (like specific heat capacity is heat capacity/mass).

Specific work = W/m = pm/(m(rho)) = p/(rho)
0
#7
(Original post by Ruthless Dutchman)
It says above that Work Done = Force x Distance, where distance is from A to B

Pressure (p) = Force (F) / cross sectional area (A), therefore F=pA

I'm not too sure what's happening with the pA(V/A) bit, but if you've been given the mass flow rate 'm' then you know that m=ρAV, so rearranging gives V=m/(ρA)

The next part shows that Work done = pA(m/ρA) but then the A that I highlighted previously seems redundant? Somebody let me know if I missed something there.

But now the cross sectional areas can cancel out to give Work Done = pm/ρ

EDIT: Actually I'm still wondering how they got Velocity/Cross sectional area from Distance :/

EDIT 2: If 'm' is actually for Mass let me know that as well, although it wouldn't really make sense for it not to
thanks for ur help too
0
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