Ineed !
1. a train is moving at 23 m/s due east when it sounds a blast on its horn, frequency = 164 hz. what frequency is heard by the driver of a car moving due east at 15 m/s along a road parallel to the tracks? use 343 m/s for the speed of sound. show all work.
2. a laser beam from earth is reflected back from a mirror on the moon in 2.60 s. if the
distance between earth and the moon is 3.85 × 108 m, calculate the speed of light.
show all work.

1. 168.1 Hz

To find the apparent frequency heard by the driver in the car, we can use the formula for the Doppler effect:

where

f is the original sound of the horn

v is the speed of sound

is the velocity of the observer (the driver and the car), which is positive if the observer is moving towards the source and negative if it is moving away

is the velocity of the sound source (the train), which is positive if the source is moving away from the observer and negative otherwise

In this problem we have, according to the sign convention used:

Substituting, we find:

2.  

The speed of light can be calculated as

where

d is the distance travelled

t is the time taken

In this problem:

is the total distance travelled by the laser beam (twice the distance between the Earth and the Moon)

t = 2.60 s is the time taken

Substituting in the formula,

d is the correct answer

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.