Figure 21.55 shows how a bleeder resistor is used to discharge a capacitor after an electronic device is shut off allowing a person to work on the electronics with less risk of shock, (a) What is the time constant? (b) How long will it take to reduce the voltage on the capacitor to 0.250% (5% of 5%) of its full value once discharge begins? (c) If the capacitor is charged to a voltage V 0 through a 100-O resistance, calculate the time it takes to rise to 0. 865V 0 (This is about two time constants.)
Figure 21.55 shows how a bleeder resistor is used to discharge a capacitor after an electronic device is shut off allowing a person to work on the electronics with less risk of shock, (a) What is the time constant? (b) How long will it take to reduce the voltage on the capacitor to 0.250% (5% of 5%) of its full value once discharge begins? (c) If the capacitor is charged to a voltage V 0 through a 100-O resistance, calculate the time it takes to rise to 0. 865V 0 (This is about two time constants.)
Figure 21.55 shows how a bleeder resistor is used to discharge a capacitor after an electronic device is shut off allowing a person to work on the electronics with less risk of shock, (a) What is the time constant? (b) How long will it take to reduce the voltage on the capacitor to 0.250% (5% of 5%) of its full value once discharge begins? (c) If the capacitor is charged to a voltage V0through a 100-O resistance, calculate the time it takes to rise to 0.865V0(This is about two time constants.)
The de-excitation of a state occurs by competing emission and relaxation processes. If the relaxation mechanisms are very effective:a) the emission of radiation is largeb) the emission of radiation is smallc) the emission occurs at a shorter wavelengthd) the de-excitation occurs only by emission processes
m
C
A block of mass m slides down a ramp of height hand
collides with an identical block that is initially at rest.
The two blocks stick together and travel around a loop of
radius R without losing contact with the track. Point A is
at the top of the loop, point B is at the end of a horizon-
tal diameter, and point C is at the bottom of the loop, as
shown in the figure above. Assume that friction between
the track and blocks is negligible.
(a) The dots below represent the two connected
blocks at points A, B, and C. Draw free-body dia-
grams showing and labeling the forces (not com
ponents) exerted on the blocks at each position.
Draw the relative lengths of all vectors to reflect
the relative magnitude of the forces.
Point A
Point B
Point C
(b) For each of the following, derive an expression in
terms of m, h, R, and fundamental constants.
i. The speed of moving block at the bottom of
the ramp, just before it contacts the stationary
block
ii. The speed of the two blocks immediately…
The velocity of an elevator is given by the graph shown.
Assume the positive direction is upward.
Velocity (m/s)
3.0
2.5
2.0
1.5
1.0
0.5
0
0
5.0
10
15
20
25
Time (s)
(a) Briefly describe the motion of the elevator.
Justify your description with reference to the
graph.
(b) Assume the elevator starts from an initial position
of y = 0 at t=0. Deriving any numerical values
you
need from the graph:
i. Write an equation for the position as a
function of time for the elevator from
t=0 to t = 3.0 seconds.
ii. Write an equation for the position as a
function of time for the elevator from t = 3.0
seconds to t = 19 seconds.
(c) A student of weight mg gets on the elevator
and rides the elevator during the time interval
shown in the graph. Consider the force of con-
tact, F, between the floor and the student. How
Justify your answer with reference to the graph
does F compare to mg at the following times?
and your equations above.
i. = 1.0 s
ii. = 10.0 s
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