Explain why you cannot cool your kitchen by leaving your refrigerator door open on a hot day. (Why does turning on a room air conditioner cool down the room, but opening a refrigerator door does not?)

Will two limp pieces of paper held a few inches apart come closer together or move farther apart if you blow between them? Explain.\s* Q31. A gust of wind blows sideways across an open outward-swinging door. Will the door slam shut or swing open as a result of this? Explain.

The 80-kg ventilation door OD with mass center at G is held in the open position shown by means of a moment M applied at A to the opening linkage. Member AB is parallel to the door for the $30^{\circ}$ position shown. Determine M.

The A-36 steel bolt is tightened within a hole so that the reactive torque on the shank AB can be expressed by the equation

$$t = (kx^{2/3}) N · m/m,$$

where x is in meters. If a torque of T = 50 N · m is applied to the bolt head, determine the constant k and the amount of twist in the 50-mm length of the shank. Assume the shank has a constant radius of 4 mm.

Colorful fireworks often involve the decomposition of barium nitrate and potassium chlorate and the reaction of the metals magnesium, aluminum, and iron with oxygen. (a) Write the formulas of barium nitrate and potassium chlorate. (b) The decomposition of solid potassium chlorate leads to the formation of solid potassium chloride and diatomic oxygen gas. Write an equation for the reaction. (c) The decomposition of solid barium nitrate leads to the formation of solid barium oxide, diatomic nitrogen gas, and diatomic oxygen gas. Write an equation for the reaction. (d) Write separate equations for the reactions of the solid metals magnesium, aluminum, and iron with diatomic oxygen gas to yield the corresponding metal oxides. (Assume the iron oxide contains $\mathrm{Fe}^{3+}$ ions.)

Two small children, Daniel and Christine, were playing a game to see who would be the first to reach the door. The children started the game by standing 20 meters away from the door, and then they each alternated doing the following:

i. Daniel moved one-half the distance between himself and the door on each move.

ii. Christine moved 1 meter toward the door on each move.

(a) How far was each child from the door after the first move?

(b) After four moves, was Daniel or Christine closer to the door? Show your work.

(c) Daniel thought that the game was unfair because he would never reach the door. Explain why his statement is correct or incorrect.

Suppose that the force is applied perpendicular to the torque arm. Given: $\tau=35.7\ \mathrm{lb}\ \mathrm{ft}$ $r=0.0240 \mathrm{ft}$

$$F= ?$$

Getting into a car involves these steps. Open the car door. Sit down. Close the door. Buckle the seat belt. Describe the steps you take in getting out of a car. How are they related to the steps involved in getting into a car?

A cylindrical pressure vessel having a radius $r=14\ \text{in.}$ and wall thickness $t=0.5\ \text{in.}$ is subjected to internal pressure $p=375\ \text{psi}$. In addition, a torque $T=90\ \mathrm{kip}- \mathrm{ft}$ acts at each end of the cylinder. (a) Determine the maximum tensile stress $\sigma_{\max }$ and the maximum in-plane shear stress $\tau_{\operatorname{mix}}$ in the wall of the cylinder. (b) If the allowable in-plane shear stress is $4.5\ \mathrm{ksi}$, what is the maximum allowable torque $T$ ? (c) If $T=150\ \mathrm{kip-ft}$ and allowable in-plane shear and allowable normal stresses are $4.5\ \mathrm{ksi}$ and $11.5\ \mathrm{ksi}$, respectively, what is the minimum required wall thickness?

A heat flux meter attached to the inner surface of a 3 -cm-thick refrigerator door indicates a heat flux of $32 \mathrm{~W} / \mathrm{m}^2$ via the door. Also, the temperatures of the inner and the outer surfaces of the door are measured to be $7^{\circ} \mathrm{C}$ and $15^{\circ} \mathrm{C}$, respectively. Find the average thermal conductivity of the refrigerator door.

A ______ is the complete set of genes in a population

In the earlier example given, was treated the merry-go-round plus child as a system (shown in the given figure) whose angular momentum is conserved. The merry-go-round is initially at rest, so its initial angular momentum is zero, but at the end it is rotating, so its final angular momentum is nonzero. The angular momentum of the merry-go-round alone thus changes, which can only happen if there is a torque on the merry-go-round. What force provides this torque?

(a) The force of gravity on the merry-go-round

(b) The force of air drag on the merry-go-round

(c) The force produced by the child when she jumps off

(d) The force of friction at the axle of the merry-go-round

A flow calorimeter is a device used to measure the specific heat of a liquid. Energy is added as heat at a known rate to a stream of the liquid as it passes through the calorimeter at a known rate. Measurement of the resulting temperature difference between the inflow and the outflow points of the liquid stream enables us to compute the specific heat of the liquid. Suppose a liquid of density $0.85 \mathrm{~g} / \mathrm{cm}^3$ flows through a calorimeter at the rate of $8.0 \mathrm{~cm}^3 / \mathrm{s}$. When energy is added at the rate of $250 \mathrm{~W}$ by means of an electric heating coil, a temperature difference of $15 \mathrm{C}^{\circ}$ is established in steady-state conditions between the inflow and the outflow points. What is the specific heat of the liquid?

When the growth of a spherical cell depends on the flow of nutrients through the surface, it is reasonable to assume that the growth rate, $d V / d t$, is proportional to the surface area, S. Assume that for a particular cell $d V / d t=\dfrac{1}{3} \cdot S$. At what rate is its radius $r$ increasing?