Spherical Mirrors: Sometimes when you look into a curved mirror you see a magnified image (a great big you) and sometimes you see a diminished image (a little you). If you look at the bottom (convex) side of a shiny spoon, what will you see?
A. You won't see an image of yourself because no image will be formed.
B. You will see a little you, upside down.
C. You will see a little you, right side up.
D. You will see a little you, but whether you are right side up or upside down depends on how near you are to the spoon.
E. You will either see a little you or a great big you, depending on how near you are to the spoon.
Answer: C
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Force on a Wire: The magnetic force on a current-carrying wire in a magnetic field is the strongest when
A. the current is in the direction of the magnetic field lines. B. the current is in the direction opposite to the magnetic field lines. C. the current is at a 180° angle with respect to the magnetic field lines. D. the current is perpendicular to the magnetic field lines. E. the current is at a 0° angle with respect to the magnetic field lines.
A horizontal force acts on a block that is initially at rest but free to move across a smooth horizontal surface. The work done by this force ________ (increases; does not change; decreases) the kinetic energy of the block.
Fill in the blank(s) with the appropriate word(s).
Surface hardening of metallic machine components, such as ball and roller bearings, is carried out in a heat treatment process where the surface temperature is increased to a desirable level without altering the internal temperature substantially. In one such operation, steel ball (spherical) bearings with a diameter of 25 mm, initially at 25°C, are immersed in a very high temperature (1000°C) molten electrolyte-solution bath and quickly removed when the temperature at a depth of 1 mm from the outer surface of the steel ball attains 725°C. If the convective heat transfer coefficient between the steel ball and the bath liquid is assumed to be 4.95 kW/(m2 K), determine the time required for attaining the surface hardening condition.
GIVEN
Steel ball bearing diameter (d)= 25 mm=0.025 m
Initial temperature (To) = 25°C
Temperature of electrolyte solution (T?) = 1000°C
The heat transfer coefficient (hc) = 4.95 kW/(m2 K) = 4950 W/(m2 K)
Radius of the surface where temperature of 7250C is attained= 11.5 mm
FIND
Time required for attaining temperature of 7250C at depth of 1 mm from outer surface.
ASSUMPTIONS
constant bath temperature, thermal properties and heat transfer coefficient
SKETCH
Which of the following has virtually no effect on the structure of a planet?
A) its composition B) its size C) its magnetic field D) its mass