Question

. Inside of a calorimeter (insulated container) is placed 200g of water at 20°C. The lid of the calorimeter is briefly lifted and 50g of lead is added initially at 200°C. What is the thermal equilibrium temperature? (3pts)

10. An object of mass 50kg is pushed in the +x direction with a force of 40N flat along a horizontal surface causing a net acceleration of 0.15m/s2 in the +x direction. What is the coefficient of kinetic friction between the surface and the object?

Answer 1

Suppose the final temperature is T.

Now Using energy conservation:

Heat gained by 0.200 kg water = Heat released by 0.050 kg lead

Q1 = Q2

m1*C1*dT1 = m2*C2*dT2

dT1 = Tf - Ti = T - 20

dT2 = 200 - T

m1 = mass of water = 200 gm = 0.200 kg

m2 = mass of lead = 50 gm = 0.050 kg

C1 = Specific heat capacity of water = 4186 J/kg.C

C2 = Specific heat capacity of lead = 128 J/kg.C

m1*C1*dT1 = m2*C2*dT2

0.200*4186*(T - 20) = 0.050*128*(200 - T)

T = (0.050*128*200 + 0.200*4186*20)/(0.200*4186 + 0.050*128)

T = 21.36 C = final thermal equilibrium temperature

Part B.

Using Force balance in horizontal direction:

Fx_net = F_app - Ff

m*a = F_app - *m*g

= (F_app - m*a)/(m*g)

Using given values:

= (40 - 50*0.15)/(50*9.81)

= Coefficient of kinetic friction = 0.066