30four boxes of increasing size and weight must be pushed up a ramp. to push the boxes at the same speed, what must you do? a) push the boxes with the same force, smoothly up the ramp.. b) the larger and heavier the box, the more force you must use when pushing. c) push the boxes with the same force, at exactly the same speed, up the ramp. d) push the largest box with the most force; push the others with about the same force.

answer: semi-infinite solid initially at a uniform temperature of 400 ◦c is cooled at its surface by convection. the cooling fluid at a constant temperature of 200 ◦c has a convective coefficient (ha) of 250 w/m2.k. the physical properties of the solid: k = 20 w/m.k and α = 4 * 10-5  m2/s. using δx = 0.04 m and δt = 10 s. write the finite difference equations describing the transient heat transfer of the first five δx and the temperature profile after 30 s.