Barbara places an object in front of a mirror. The mirror produces an image that is inverted, real, and smaller than the object.

Which kind(s) of mirror could Barbara be using?

convex, because concave and plane mirrors produce only virtual images
concave, because plane and convex mirrors produce only upright virtual images
concave or convex, because both types of mirrors produce images that are inverted and real
convex or plane, because both types of mirrors produce an image that is smaller than the object

An insulated 40 ft^3 rigid tank contains air at 50 psia and 120°f. a valve connected to the tank is now opened, and air is allowed to escape until the pressure inside drops to 25 psia. the air temperature during this process is kept constant by an electric resistance heater placed in the tank. determine the electrical work done during this process.

In an old-fashioned amusement park ride, passengers stand inside a 3.0-m-tall, 5.0-m-diameter hollow steel cylinder with their backs against the wall. the cylinder begins to rotate about a vertical axis. then the floor on which the passengers are standing suddenly drops away! if all goes well, the passengers will “stick” to the wall and not slide. clothing has a static coefficient of friction against steel in the range 0.60 to 1.0 and a kinetic coefficient in the range 0.40 to 0.70. part a what is the minimum rotational frequency, in rpm, for which the ride is safe? express your answer using two significant figures. f f = rpm

The first law of thermodynamics is as follows: ∆u=q-w , which means in a system is equal to added, minus done by the system. the units for these variables are in .