What does wave speed have to do with all SONAR AND RADAR technologies?
2 answers:
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Answer:
6.86 m/s
Explanation:
This problem can be solved by doing the total energy balance, i.e:
initial (KE + PE) = final (KE + PE). { KE = Kinetic Energy and PE = Potential Energy}
Since the rod comes to a halt at the topmost position, the KE final is 0. Therefore, all the KE initial is changed to PE, i.e, ΔKE = ΔPE.
Now, at the initial position (the rod hanging vertically down), the bottom-most end is given a velocity of v0. The initial angular velocity(ω) of the rod is given by ω = v/r , where v is the velocity of a particle on the rod and r is the distance of this particle from the axis.
Now, taking v = v0 and r = length of the rod(L), we get ω = v0/ 0.8 rad/s
The rotational KE of the rod is given by KE = 0.5Iω², where I is the moment of inertia of the rod about the axis of rotation and this is given by I = 1/3mL², where L is the length of the rod. Therefore, KE = 1/2ω²1/3mL² = 1/6ω²mL². Also, ω = v0/L, hence KE = 1/6m(v0)²
This KE is equal to the change in PE of the rod. Since the rod is uniform, the center of mass of the rod is at its center and is therefore at a distane of L/2 from the axis of rotation in the downward direction and at the final position, it is at a distance of L/2 in the upward direction. Hence ΔPE = mgL/2 + mgL/2 = mgL. (g = 9.8 m/s²)
Now, 1/6m(v0)² = mgL ⇒ v0 =
Hence, v0 = 6.86 m/s
With the addition of vectors we can find that the correct answer is:
C) Q> P > R = S > T
The addition of vectors must be done taking into account that they have modulus and direction. The analytical method is one of the easiest methods, the method to do it is:
- Set a Cartesian coordinate system
- Decompose vectors into their components in a Cartesian system
- Perform the algebraic sums on each axis
- Find the resultant vector using the Pythagoras' Theorem to find the modulus and trigonometry to find the direction.
In this exercise indicate that the modulus of all vectors is the same, suppose that the value of the modulus is A.
We fix a Cartesian coordinate system with the horizontal x axis and the vertical y axis, we can see that we do not need to perform any decomposition, so we perform the algebraic sums
Diagram P
x-axis
x = 2A
y-axis
y = 2A
The modulus of the resulting vector can be found with the Pythagorean Theorem
P =
P =
P = 2 √2 A
Diagram Q
x-axis
x = 3A
y-axis
y = A
Resulting
Q =
Q =
Q =
Diagram R
x- axis
x = 0
y-axis
y = 2 A
Resulting
R =
R =
Diagram S
x-axis
x = 2 A
y-axis
y = 0
Resulting
S = 2A
Diagram T
x- axis
x = 0
y-axis
y = 0
Resultant T = 0
We order the diagram from highest to lowest
Q> P> R = S> T
When reviewing the different answers, the correct one is:
C. Q> P> R = S> T
Learn more about adding vectors here: