Suppose that 250.0 g of a material with the specific heat capacity c = 0.237 cal

Question

Suppose that 250.0 g of a material with the specific heat capacity c = 0.237 cal/g/degree C is heated by a flame until its temperature increases by 10.1 degree C. How much energy has it absorbed? Suppose that a force of 20.4 N acts through and parallel to a displacement of 135.2 m on an object with mass 5.8 kg. If the only effect was to increase its speed from an initial value of zero, how fast would it now be going? Suppose that the force in Exercise 2 is applied to the object, which in this exercise starts off with a velocity, but does not cause an acceleration. Clearly there would need to be at least one other force involved - an example would be if the 20.4 N force acted horizontally on a 5.8 kg box sliding at a steady speed across a floor. In this case, how much work was done by the force?

Explanation / Answer

Exercise 1)

m = 250 g = 0.250 kg

c = 0.237 cal/g/C = 0.237*4.186 J /10^-3 kg /C =992.082 J/kg-C

dT = 10.1 C

then Q = m*c*dT = 0.25*992.082*10.1 = 2505 J

Exercise 2) Work doen by the ent force = change in KE

W = F*S* = 0.5*m*v^2

20.4*135.2 = 0.5*5.8*v^2

v = 30.83 m/s

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Exercise 3)

since the box is steadily sliding

accelaration a = 0 m/s^2

the opposite force to 20.4 N should be = 20.4 N

Work done by the net force = 20.4*135.2 = 2758 J

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