Question

Celine's lipstick wears off at a constant rate through the day. When she first puts it on, it is 1 mm thick, and she always catches it when it gets down to being just 0.1 mm thick and puts more on. What is the probability at any given time that she will have between 0.3 and 0.4 mm on? Remember that no amount is any more likely than any other.

Answer 1

a)
we know, thermal conductivity og window glass, k_glass = 0.96 W/(m k )

Rate of heat being lost, dQ/dt = k*A*dT/L

= 0.96*1.4*2.5*(20.5 - (-15))/(5.8*10^-3)

= 2.06*10^4 W   <<<<<<<<------------Answer

b)

when paper layer is used,

the heat flux through the glass must be equal to the heat flux through the paper at steady state.

k_glass*(T_interior - T_interface)/t_glass = k_paper*(T_interfcae - T_out)/t_paper

0.96*(20.5 - T)/0.0058 = 0.05*(T - (-15))/0.00075

==> T = 10.3 degrees celsius

so, the rate of heat lost, dQ/dt = k_glass*A*(T_interior - T_interfcae)/t_glass

= 0.96*(20.5 - 10.3)*1.4*2.5/(5.8*10^-3)

= 5.90*10^3 W <<<<<<<<--------------------------Answer