When an alpha particle is emitted from an unstable nucleus, the atomic mass number of the nucleus
A) increases by 2.
B) decreases by 4.
C) stays unchanged.
D) increases by 4.
E) decreases by 2.
B
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In a problem using energy considerations to solve for the speed of a ball thrown from the top of a building when it strikes the ground below, where should the potential energy have its zero value?
a. It should be at the level from where the ball is thrown. b. It should be at the ground level where the ball hits. c. It should be slightly below ground level so the potential energy is always positive. d. It doesn't matter since only differences in potential energy matter in solutions.
Calculate the net radiant-heat-transfer rate if the two surfaces in Problem 11.18 are black and are connected by a refractory surface with an area of 500 m2. A1 is at 555 K and A2 is at 278 K. What is the refractory surface temperature?
GIVEN
• Rectangular surfaces A1 and A2 connected by a refractory surface A3
• A1 is parallel to and centered 5 m above A2
• Dimensions of A1 = 1 m × 20 m
• A2 is 20 m2
• A3 is 500 m2
• Temperature of A1 (T1) = 555 K
• Temperature of A2 (T2) = 278 K
• A1 and A2 are black
FIND
(a) The net radiating heat transfer rate (q1)
(b) The refractory surface temperature (T3)
SKETCH
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant (?) = 5.67 × 10–8 W/(m2 K4)
A uniform linear charge of 3.0 nC/m is distributed along the y axis from y = ?3 m to y = 2m. Which of the following integrals is correct for the magnitude of the electric field at y = 4 m on the y axis?
A.
B.
C.
D.
E.
An uniform electric field of magnitude E = 100 N/C is oriented along the positive y-axis. What is the magnitude of the flux of this field through a square of surface area A = 2 m2 oriented parallel to the yz-plane?
A) 200 Nm2/C B) 100 Nm2/C C) 0 D) 400 Nm2/C E) 600 Nm2/C