Author Question: Is the conductive heat flow rate the greatest, about the middle value, or the least amount of total ... (Read 43 times)

bb · **on:** Jul 28, 2018

Is the conductive heat flow rate the greatest, about the middle value, or the least amount of total heat flow through the window when both convection and conduction are important? Explain.

What will be an ideal response?

Question 2

A pulley system holding a rope that is pulled out a distance of 20 m is used for lifting a 2500 kg grand piano. The piano can be raised 3 m by application of a 375 N force to the rope.

What will be an ideal response?

xoxo123 · **Reply #1 on:** Jul 28, 2018

Answer to Question 1

Radiation is the predominant pathway for energy loss through windows. Both
conduction and convection play roles (see Extension 9.4), but these are less important to
heat loss than radiative losses through the windowpanes.

Answer to Question 2

The weight of the piano is 2500 kg x 10 m/s2 = 25,000 N. To lift the piano 3 m,
an amount of work 25,000 N x 3 m = 75,000 J must be done. The maximum amount of
work that can be done by the 375 N force raised through 20 m is 375 N x 20 m = 7,500 J.
This is far too little to do the work to raise the piano.
The piano can only be made to raise at most by 0.3 m, because 25,000 N x 0.3 m = 7,500
J.