Given:
A pilot can travel 450 miles with the wind in the same amount of time as 360 miles against the wind.
Pilot's speed in still air is 315 miles per hour.
To find:
The speed of the wind.
Solution:
Let the speed of wind be x miles per hour.
Speed with wind = 315+x miles per hour
Speed against wind = 315-x miles per hour
We know that,
According to the question,
Divide both sides by 90.
By cross multiplication, we get
Divide both sides by 9.
Therefore, the speed of wind is 35 miles per hour.
Answer:
4.1 N
Step-by-step explanation:
We can solve this problem by using considerations about energy.
At the moment the stone is dropped, it has only gravitational potential energy:
where
is the weight of the stone
h = 10 m is the initial height of the stone
As the stone falls, part of this energy is converted into kinetic energy, while part into thermal energy due to the presence of the air friction, acting opposite to the motion of the stone:
where:
is the mass
v = 13 m/s is the final speed of the stone
is the thermal energy
The thermal energy is actually equal to the work done by the air friction on the stone:
where
F is the average force of friction
h = 10 m
Since the total energy must be conserved, we can combine the three equations, so we find:
And solving for F, we find the average force of air friction: