Jack and Jill are both traveling straight north. Jack is walking at 4 mph, while Jill is riding a bicycle at 12 mph. Regarding their speeds and velocities:
A) they both have the same speed and the same velocity.
B) they have different speeds and different velocities.
C) they both have the same speed but different velocities.
D) they have different speeds, but the same velocity.
E) None of the above.
B
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Two 1.5 m-square and parallel flat plates are 30 cm apart. Plate A1 is maintained at a temperature of 1100 K and A2 at 500 K. The emissivities of the plates are 0.5 and 0.8, respectively. Considering the surroundings black at 0 K and including multiple inter-reflections, determine (a) the net radiant exchange between the plates and (b) the heat input required by surface A1 to maintain its temperature. The outer-facing surfaces of the plates are adiabatic.
GIVEN
? Two square parallel flat plates, 30 cm apart
? Temperature of A1 (T1) = 1100 K
? Temperature of A2 (T2) = 500 K
? Emittances: ?1 = 0.5 ?2 = 0.8
? Surroundings are black at (T3) = 0 K
FIND
Including multiple inter-reflections, determine:
(a) The net radiant exchange (q1–2)
(b) The heat input at surface A1 (q1) required to maintain its temperature
SKETCH
PROPERTIES AND CONSTANTS
Mass on a Spring: A mass on a spring undergoes SHM. When the mass passes through the equilibrium position, which of the following statements about it are true? (There could be more than one correct choice.)
A. Its acceleration is zero. B. Its speed is zero. C. Its elastic potential energy is zero. D. Its kinetic energy is a maximum. E. Its total mechanical energy is zero.
A wave of frequency of 1000 hertz vibrates at
A) less than 1000 cycles per second. B) 1000 cycles per second. C) more than 1000 cycles per second. D) none of the above
The force due to gravity between two objects can be described using the equation Fg = G M1 M2 / d2. In this equation, what does G represent?
A) the distance between the two objects B) the universal gravitational constant C) the density of the smaller object