- #1

chrispsu

- 23

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Hey just two questions i need a little bit of homework help on...they just aren't clicking and maybe I am just approaching them the wrong way. A good way to start or any help would be greatly appreciated for them. Thanks :)

The pressure question: A 0.13 kg balloon is filled with helium (density = 0.179 kg/m3). If the balloon is a sphere with a radius of 4.6 m, what is the maximum weight it can lift?

at first i was thinking P=F/A and that pressure was equal to density*9.8*height

but i don't know what the height would be and i can't figure out what else would work?

The thermo question:

A ceramic coffee cup, with m = 105 g and c = 1090 J/(kgK), is initially at room temperature (24.0°C). If 175 g of 80.3°C coffee and 12.2 g of 5.00°C cream are added to the cup, what is the equilibrium temperature of the system? Assume that no heat is exchanged with the surroundings, and that the specific heat of coffee and cream are the same as the specific heat of water.

i kno q=mc(tf-ti) and that the q would be equal so mctf-ti(coffeecup)= mctf-ti(coffee) + mctf-ti(cream)

and then solving for change in temp to add to the temps already given. but i can't get a change in t.

The pressure question: A 0.13 kg balloon is filled with helium (density = 0.179 kg/m3). If the balloon is a sphere with a radius of 4.6 m, what is the maximum weight it can lift?

at first i was thinking P=F/A and that pressure was equal to density*9.8*height

but i don't know what the height would be and i can't figure out what else would work?

The thermo question:

A ceramic coffee cup, with m = 105 g and c = 1090 J/(kgK), is initially at room temperature (24.0°C). If 175 g of 80.3°C coffee and 12.2 g of 5.00°C cream are added to the cup, what is the equilibrium temperature of the system? Assume that no heat is exchanged with the surroundings, and that the specific heat of coffee and cream are the same as the specific heat of water.

i kno q=mc(tf-ti) and that the q would be equal so mctf-ti(coffeecup)= mctf-ti(coffee) + mctf-ti(cream)

and then solving for change in temp to add to the temps already given. but i can't get a change in t.

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