When 68 j of energy are added to a sample of gallium that is initially 25c, the temperature rises to 38c. what is the volume of the sample?

With the input of 68 J of energy, the temperature rises by 13 K, and the molar heat capacity of gallium is 25.86 J/(mol*K)  
68 J * 25.86 J/(mol·K) * x mol=13 K 
x=13/(68*25.86)=0.00739 mol  
Molar mass of gallium is 69.723 g/mol, making the mass of this sample 0.515 g of gallium: 
0.151 g = 68.723 g/mol * 0.00739 mol  
The density of gallium is 5.91 g/cm^3, making the volume of this sample
0.872 cm^3 of gallium:
 0.872 cm^3 = (0.515 g) / (5.91 g/cm^3)

Answer: fn = wcos50 = 38.89(9.81)(cos50) = 245.23 n