Alguien sepa como hacer éstos
1 answer:
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Answer:
The friction force is 250 N
Explanation:
The desk is moving at constant velocity. This means that its acceleration is zero: a = 0. Newton's second law states that the resultant of the forces acting on the desk is equal to the product between mass (m) and acceleration (a):
In this case, we know that the acceleration is zero: a = 0, so also the resultant of the forces must be zero:
(1)
We are only interested in the forces acting along the horizontal direction, since it is the direction of motion. There are two forces acting in this direction:
- the pull, forward, F = 250 N
- the friction force, backward,
Given (1), we have
So the force of friction must be equal to the pull:
Answer:
25.5 m/s
Explanation:
The Doppler effect occurs when there is relative motion between a source of a wave and an observer. In such situation, there is a shift in the apparent frequency of the wave perceived by the observer.
The formula that gives the apparent frequency perceived by the observer is:
where
f is the real frequency of the wave
f' is the apparent frequency of the wave
v is the speed of the wave
is the velocity of the source (negative if the source is moving towards the observer, positive otherwise)
is the velocity of the observer (positive if the observer is moving towards the source, negative otherwise)
In this problem:
v = 340 m/s is the speed of sound
f = 800 Hz is the frequency of the horn
f' = 860 Hz is the apparent frequency
(the observer is at rest)
Re-arranging the equation for , we can find the velocity of the horn and the driver:
So, 25.5 m/s towards the observer.