A particle (m = 20 mg, q = ?5.0 ?C) moves in a uniform electric field of 60 N/C in the positive x direction. At t = 0, the particle is moving 25 m/s in the positive x direction and is passing through the origin. How far is the particle from the origin at t = 2.0 s?
a. 80 m
b. 20 m
c. 58 m
d. 10 m
e. 30 m
b
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The diagram below is an H-R diagram. The line indicates the location of the main sequence. Which of the five labeled locations on the H-R diagram indicates a luminosity and temperature similar to that of a T Tauri star?
Wave period is the reciprocal of
a. amplitude. b. frequency. c. wave velocity. d. all of these.
An electronic circuit board is the shape of a flat plate 0.3 m × 0.3 m in plan-form and dissipates 15 W. It is placed in operation on an insulated surface in a horizontal position or at an angle of 45 degrees to horizontal, in both cases; it is in still air at 25°C. If the circuit fails above 60°C, determine if the two proposed installations are safe.
GIVEN
• A flat plate with insulated back, horizontal or at an angle of 45 degrees in still air
• Plate size (s × s) = 0.3 m × 0.3m
• Heat generation rate (qG) = 15 W
• Air temperature (T?) = 25°C
• Maximum plate temperature (Ts) = 60°C
FIND
• If the two plate positions are safe
ASSUMPTIONS
• Radiative heat transfer is negligible
SKETCH
PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 43°C
Thermal expansion coefficient (?) = 0.00316 1/K
Thermal conductivity (k) = 0.0267 W/(m K)
Kinematic viscosity (?) = 17.9 × 10–6 m2/s
Prandtl number (Pr) = 0.71
A person is nearsighted with a near point of 75. cm. (a) What FOCAL LENGTH is this? (b) What POWER lens is needed to correct their nearsightedness (assuming distance from lens to eye is negligible)?
What will be an ideal response?