Question

A ice box of styrofoam (thermal conductivity = `0.01` J `ms^(-1)K^(-1)`) is used to keep liquid cool. It has a total wall area, including lid, of `10.8 m^(2)` and wall thickness of `2.0` cm. A bottle of water is placed in the box and filled with ice. If the outside temperature is `30^(@)C`, the rate of flow of heat into the box is (in `J//s)`
A. 16
B. 14
C. 12
D. 10

Answer 1

Correct Answer - C
Here `K=0.01 J ms^(-1)K^(-1), A=0.8 m^(2)`,
`Delta x=2 cm =2xx10^(-2)m`
`Delta T=30^(@)C, dQ//dt=?`
`(dQ)/(dt) =KA (Delta T)/(Delta x)=0.01xx0.8xx(30)/(2xx10^(-2))`
`=(8)/(1000)xx(30)/(2)xx100 =12 J//s`