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Answer:
Apparent frequency increases for Bob and decreases for Jill.
Explanation:
Doppler effect refers to the apparent change in frequency when there is relative motion between source and the listener. When the source and listener move closer, the apparent frequency heard by the listener increases. And when the source and listener move away from each other, the apparent frequency heard by the listener decreases.
Thus, when the emergency vehicle approaches Bob, the apparent frequency of the siren increases. It moves away from Jill, the apparent frequency heard by the Jill decreases.
Answer:
D. Opening the front door in winter to filter and clean warm ai
Explanation:
All of the following are examples of ways to improve energy efficiency of heating systems, except _______.
A. Closing off rooms that aren’t in use.
B. Frequently cleaning the furnace filter.
C. Fixing cracks in the walls and floor.
D. Opening the front door in winter to filter and clean warm air
for an heating systems it is better to keep the front door shut so that all the heat energy does not escape outside.
when heat energy is within a closed system ,it can still be utilized to keep the inhabitants warm otherwise there will be an exchange with the cold from winter fall outside the air, and the heating system's efficiency will be reduced
Answer:
Approximately
upwards (assuming that
.)
Explanation:
External forces on this astronaut:
- Weight (gravitational attraction) from the earth (downwards,) and
- Normal force from the floor (upwards.)
Let
denote the magnitude of the normal force on this astronaut from the floor. Since the direction of the normal force is opposite to the direction of the gravitational attraction, the magnitude of the net force on this astronaut would be:
.
Let
denote the mass of this astronaut. The magnitude of the gravitational attraction on this astronaut would be
.
Let
denote the acceleration of this astronaut. The magnitude of the net force on this astronaut would be
.
Rearrange
to obtain an expression for the magnitude of the normal force on this astronaut:
.
downward force then reaction if you mean what forces