In research in cardiology and exercise physiology, it is often important to know the mast of blood pumped by a person’s bran in one stroke. This information can be obtained by means of a ballistocardiograph . The instrument works as follows: The subject lies on a horizontal pallet floating on a film of air. Friction on the pallet is negligible. Initially, the momentum of the system is zero. When the heart beats, it expels a mass m of blood into the aorta with speed v , and the body and platform move in the opposite direction with speed V . The speed of the blood tan be determined independently (e.g., by observing an ultrasound Doppler shift). Assume that the blood’s speed is 50.0 cm/s in one typical trial. The mass of the subject plus the pallet is 54.0 kg. The pallet moves at a speed of 6.00 × 10 −5 m in 0.160 s after one heartbeat. Calculate the mass of blood that leaves the heart. Assume that the mass of blood is negligible compared with the total mass of the person. This simplified example illustrates the principle of ballistocardiography, but in practice a more sophisticated model of heart function is used.
In research in cardiology and exercise physiology, it is often important to know the mast of blood pumped by a person’s bran in one stroke. This information can be obtained by means of a ballistocardiograph . The instrument works as follows: The subject lies on a horizontal pallet floating on a film of air. Friction on the pallet is negligible. Initially, the momentum of the system is zero. When the heart beats, it expels a mass m of blood into the aorta with speed v , and the body and platform move in the opposite direction with speed V . The speed of the blood tan be determined independently (e.g., by observing an ultrasound Doppler shift). Assume that the blood’s speed is 50.0 cm/s in one typical trial. The mass of the subject plus the pallet is 54.0 kg. The pallet moves at a speed of 6.00 × 10 −5 m in 0.160 s after one heartbeat. Calculate the mass of blood that leaves the heart. Assume that the mass of blood is negligible compared with the total mass of the person. This simplified example illustrates the principle of ballistocardiography, but in practice a more sophisticated model of heart function is used.
Solution Summary: The author explains that the mass of blood that leaves the heart is 40.5g.
In research in cardiology and exercise physiology, it is often important to know the mast of blood pumped by a person’s bran in one stroke. This information can be obtained by means of a ballistocardiograph. The instrument works as follows: The subject lies on a horizontal pallet floating on a film of air. Friction on the pallet is negligible. Initially, the momentum of the system is zero. When the heart beats, it expels a mass m of blood into the aorta with speed v, and the body and platform move in the opposite direction with speed V. The speed of the blood tan be determined independently (e.g., by observing an ultrasound Doppler shift). Assume that the blood’s speed is 50.0 cm/s in one typical trial. The mass of the subject plus the pallet is 54.0 kg. The pallet moves at a speed of 6.00 × 10−5 m in 0.160 s after one heartbeat. Calculate the mass of blood that leaves the heart. Assume that the mass of blood is negligible compared with the total mass of the person. This simplified example illustrates the principle of ballistocardiography, but in practice a more sophisticated model of heart function is used.
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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