Please help with these 2 Physics Questions

1. A sample of a solid material weighs 40 grams in air and 16 grams when immersed in water. The value of the density of the sample is ______.

2. A theoretical heat engine operating between a high-temperature reservoir at 1000 degrees Celsius and a low-temperature reservoir at 20 degrees Celsius would have a Carnot efficiency of_____%

Any help is appreciated. Thanks!

Hello

This first question is badly worded. A mass doesn't change. 40 grams is 40 grams anywhere, that's one of the first things that they teach you in physics. They should have put that a spring scale reads 16 grams when the object is immersed in water, but wouldn't the scale read Newtons, not grams?.

There is probably a simple formula for this but I don't know it. Lets call the density of the solid as Ds and the density of the water as Dw, the volume of the solid is V and the mass is M, and the apparent mass in water Ma, the buoyant force is B

Ds = M / V

and B = V * Dw

and B = M - Ma

So V = B / Dw = (M - Ma) / Dw

Ds = M / V = M * Dw / (M - Ma)

Ds = 40 grams * (1 kg / 1000 grams) * 1000 kg/m^3 / [(40 grams - 16 grams) *(1 kg / 1000 grams)]

Ds = 1667 kg/m*3

B) I believe that Carnot eff is just

n = 1 - (Tx/Th)

n = 1 - (20/1000)

n = 98 %, but that would be the max efficiency attainable not the actual efficiency.

Good Luck