A power washer is being used to clean the siding of a house. Water enters at 20 C, 1 atm, with a volumetric flow rate of 0.1 lit
er/s through a 2.5-cm-diameter hose. A jet of water exits at 23 C, 1 atm, with a velocity of 50 m/s at an elevation of 5 m. At steady state, the magnitude of the heat transfer rate from the power unit to the surroundings is 10% of the power input. Determine the power input to the motor, kW.
1 answer:
Answer:
W=1259W=1.2Kw
Explanation:
Hello!
The first step to solve is to find the enthalpies at the entrance (state 1) and the exit of the washer, for this we use the thermodynamic tables.
Through laboratory tests, thermodynamic tables were developed, these allow to know all the thermodynamic properties of a substance (entropy, enthalpy, pressure, specific volume, internal energy etc ..)
through prior knowledge of two other properties such as pressure and temperature.
state 1
h1(T=20C,P=1atm)=83.93kJ/kg
state 2
h1(T=23C,P=1atm)=96.48kJ/kg
now we find the mass flow remembering that it is the product of the flow rate by the density=
m= mass flow
q=flow=0.1l/S=0.0001M^3/s
α=Density=1000kg/m^3
m=0.1kg/s
Now we draw the energy flows in the washer (see attached image) and propose the first law of thermodynamics that states that the energy that enters must be equal to the one that comes out
where
m=mass flow
h=entalpy
v=speed
W=power input
g=gravity
H=height
SOLVING FOR W
W=1259W=1.2Kw
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Answer:
A. 0.432
B. -1.92
C. 1.44 units/second
D. -3.2 units/second
Explanation:
A. To calculate her x position, we just use the following equation of motion to find the distance traveled:
here s = displacement
t = time (in seconds)
a = acceleration
Solving for the distance, we get:
s = 0.432 m
Since 0.432 meters east is equals to 0.432 meter in the positive x-direction, the x position is also 0.432.
B. Since the skater has a constant v - velocity of -3.2 m/s, (south means negative y axis), the total distance traveled is:
Distance = speed * time = -3.2 * 0.6 = -1.92 m
The answer is -1.92 units in the y-axis.
C. The x velocity component is the final speed in the east direction, which is going to be:
v = 1.44 units/second (in positive x direction)
D. Her y velocity component does not change, since the velocity towards the south is a constant 3.2 m/s
Thus the answer is -3.2 units/second in the y-axis.
Answer:633 m
Explanation:
First we have moved 300 m in North
let say it as point a and its vector is
after that we have moved 500 m northeast
let say it as point b
therefore position of b with respect to a is
r
Therefore position of b w.r.t to origin is
after this we moved 400 m south of east i.e.
below from positive x axis
let say it as c
magnitude is
=633.052
for direction
with x -axis
Answer:
Explanation:
We must separate the motion into two parts, the first when the rocket's engines is on and the second when the rocket's engines is off. So, we need to know the height () that the rocket reaches while its engine is on and we need to know the distance (
) that it travels while its engine is off.
For solving this we use the kinematic equations:
In the first part we have:
and the final speed is:
In the second part, the final speed of the first part it will be the initial speed, and the final speed is zero, since gravity slows it down the rocket.
So, we have:
The sum of these heights will give us the total height, which is known:
This is the time that its needed in order for the rocket to reach the required altitude.