Wave #1 has frequency f1 and wavelength ?1 . Wave #2 has frequency f2 = 6 f1 and wavelength ?2 = 2?1 . How does the speed v2 of wave #2 compare with the speed v1 of wave #1?
a. v2 = 12v1 b. v2 = 6v1
c. v2 = 1.5v1 d. v2 = v1/6
a
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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
Charge of uniform density (80 nC/m3) is distributed throughout a hollow cylindrical region formed by two coaxial cylindrical surfaces of radii 1.0 mm and 3.0 mm. Determine the magnitude of the electric field at a point which is 2.0 mm from the symmetry axis.
A. 7.9 N/C B. 9.0 N/C C. 5.9 N/C D. 6.8 N/C E. 18 N/C
Three 10-ohm resistors take the shape of a triangle, one resistor in each leg. An ohm-meter across any two points of the triangle will show the equivalent resistance to be
A) 1.4 ohms. B) 5 ohms. C) 6.7 ohms. D) greater than 6.7 ohms.
Uniform Circular Motion: A car moving at a steady 10 m/s on a level highway encounters a bump that has a circular cross-section with a radius of 30 m. The car maintains its speed over the bump. What is the normal force exerted by the seat of the car on a 60.0-kg passenger when the car is at the top of the bump?
A. 200 N B. 390 N C. 790 N D. 490 N E. 590 N