A resistor R = 0.07 ?, an inductor L = 35 mH, and a capacitor C = 45 ?F are connected in series to form an LRC circuit
Starting at t = 0, when the capacitor is fully charged, how many oscillations are completed in the circuit by the time the amplitude has decreased to half it maximum? A)
206
B)
88
C)
187
D)
25
E)
44
B
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A 0.1-cm-thick square, flat copper plate, 2.5 m × 2.5 m is to be cooled in a vertical position. The initial temperature of the plate is 90°C with the ambient fluid at 30°C. The fluid medium is either atmospheric air or water.
(a) Calculate the Grashof number
(b) Determine the initial heat transfer coefficient
(c) Calculate the initial rate of heat transfer by convection
(d) Estimate the initial rate of temperature change for the plate
GIVEN
• A vertical flat copper plate in either air or water
• Plate thickness (t) = 0.1 cm = 0.001 m
• Plate dimensions (L × w) = 2.5 m × 2.5 m
• Initial plate temperature (Ts,i) = 90°C
• Ambient fluid temperature (T?) = 30°C
FIND
(a) The Grashof number (Gr)
(b) The rate of heat transfer by convection (qc)
(c) The initial rate of temperature change (dT/dt)t = 0
SKETCH
PROPERTIES AND CONSTANTS
for copper
Density (?c) = 8933 kg/m3
Specific heat (cc) = 383 J/(kg K)
Water at 60°C Air at 60°C
Imagine that an external force of 100 N must be applied to keep a bicycle and rider moving at a constant speed of 12 mi/h against opposing air drag. To double the bike’s speed to 24 mi/h, we must increase the magnitude of the force exerted on the bike to
A. 141 N B. 200 N C. 400 N D. It depends on the bike’s shape and area E. Other (specify)
A charge q = 3 × 10-6 C of mass m = 2 × 10-6 kg, and speed v = 5 × 106 m/s enters a uniform magnetic field. The mass experiences an acceleration a = 3 × 104 m/s2
What is the minimum magnetic field that would produce such an acceleration? A) 0.1 T B) 0.004 T C) 0.001 T D) 0.01 T E) 0.04 T
A 10-m plank is being moved by rolling it over two cylindrical logs placed 2 m from either end of the plank. As the plank is pushed, the logs roll on the ground without slipping, and they do not slip with respect to the plank
How far can the plank be moved before the rear log reaches the end of the plank?