Um pêndulo consiste em uma bola de massa m presa a um fio de comprimento L. A ball is pulled until the wire forms an angle θo with a vertical. So it's dropped from

rest as shown in a figure. Neglect air resistance.

a) Show that the work done by the tension in the wire is zero.

b) Voltage is the only non-conservative force acting on the system. The fact does

work done by the voltage is null, implies in the conservation of energy

mechanics? Justify!

c) Determine a literal expression for the speed of the ball at the lowest point of the

trajectory as a function of the parameters θ and L given. Tip: make a diagram of

free body to facilitate.

d) Determine a literal expression for the module of the thread tension, at the most

down the trajectory according to the parameters θ and L given. .

Tip: Make a free-body diagram for ease

Acommercial grade cubical freezer, 4 m on a side, has a composite wall consisting of an exterior sheet of 5.0-mm thick plain carbon steel (kst= 60.5 w/m k), an intermediate layer of 100-mm thick polyurethane insulation (kins 0.02 w/m k), and an inner sheet of 5.0- mm thick aluminium alloy (kal polyurethane insulation and both metallic sheets are each characterized by a thermal contact resistance of r 2.5 x 104 m2 k/w. (a) what is the steady-state cooling load that must be maintained by the refrigerator under conditions for which the outer and inner surface temperatures are 25°c and -5°c, respectively? (b) for power saving purpose, which wall material should be increased/reduced in. thickness in order to reduce 50% of the cooling load found in part (a)? redesign the thickness of the proposed material. 177 w/m-k). adhesive interfaces between the q=575.93 w