A 5-N block of wood is difficult to fully submerge in a pool of mercury because the buoyant force on the block when submerged is
A) less than 5 N.
B) 5 N.
C) much more than 5 N.
Answer: C
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Which of the following quantities is directly proportional to the time interval after a projectile has left the barrel that shot it out? The x axis is horizontal; the y axis is vertically upward.
A.
B.
C.
D.
E.
It has been proposed that highly concentrating solar power such as the one below can be used to process materials economically when it is desirable to heat the material surface rapidly without significantly heating the bulk. In one such process for case hardening low-cost carbon steel, the surface of a thin disk is to be exposed to concentrated solar flux.
The distribution of absorbed solar flux on the disk is given by
where r is the distance from the disk axis and q''max and Ro are parameters that describe
the flux distribution. The disk diameter is 2Rs, its thickness is Zs, its thermal conductivity
is k and its thermal diffusivity is a. The disk is initially at temperature Tinit and at time
t = 0 it is suddenly exposed to the concentrated flux. Derive the set of explicit difference
equations needed to predict how the disk temperature distribution evolves with time. The
edge and bottom surface of the disk are insulated and reradiation from the disk is
neglected.
GIVEN
- Steel disk exposed to concentrated solar flux
FIND
(a) Explicit difference equations that describe evolution of disk temperature
How far above the horizon is the Moon when its image reflected in calm water is completely polarized? (nwater = 1.333)
a. 53.12° b. 18.44° c. 22.20° d. 36.88°
A car is moving down a straight, steep hill. By applying the brake, the driver is able to keep the speed of the car constant. Which of the following statements is true in this situation?
A. The net acceleration is positive. B. There is a net force on the car. C. The net acceleration is negative. D. There is no net force on the car.