Star A has an apparent visual magnitude of 6.3 and star B has an apparent visual magnitude of 5.3 . Star A is ____________________ times ____________________ than star B
Fill in the blank(s) with correct word
2.5, fainter
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The most massive main-sequence stars are the ________ spectral class and the ________ luminosity class
Fill in the blank(s) with correct word
A airplane having a metal surface and a wingspan of 25.0 m flies horizontally at 200. m/s where the earth's magnetic field is vertical with magnitude 45.0 ?T
(a) What emf is induced across the wings? (b) What wingspan would the plane need to produce 1.00-V emf across its wings? (c) The plane now reverses direction. Does the polarity of the wingtip emf change? That is, if the left wing was positive before, does it now become negative?
An electronic circuit contains a power resistor that dissipates 1.5 W. The designer wants to modify the circuitry in such a way that it will be necessary for the resistor to dissipate 2.5 W. The resistor is in the shape of a disk 1 cm in diameter and 0.6-mm-thick. Its surface is aligned with a cooling air flow at 30°C and 10 m/s velocity, i.e., the vertical axis of the disc is in cross-flow with the cooling air. The resistor lifetime becomes unacceptable if its surface temperature exceeds 90°C. Is it necessary to replace the resistor for the new circuit?
GIVEN
• A heat generating resistor disk with its surface aligned with a cooling airflow
• Heat generation rate ( Q
G) = 2.5 W
• Disk diameter (D) = 1 cm = 0.01 m
• Disk thickness (t) = 0.6 mm = 0.0006 m
• Air temperature (T?) = 30°C
• Air velocity (U?) = 10 m/s
• Maximum surface temperature (Ts) = 90°C
FIND
• Is it necessary to replace the resistor?
ASSUMPTIONS
• Steady state
• Radiation is negligible
SKETCH
A 4.20-g bullet embeds itself in a 20.0-kg block, which is attached to a horizontal spring with a force constant of 980 N/m
The maximum compression of the spring is 2.40 cm. What is the speed of the bullet just before it hits the block? A) 800 m/s B) 700 m/s C) 672 m/s D) 900 m/s E) 952 m/s