Boxes A and B are in contact on a horizontal, frictionless surface. Box A has mass 21.0 kg and box B has mass 8.0 kg. A horizont
1 answer:
Answer:
2.75 N
Explanation:
Given that,
Box A has a mass 21.0 kg and box B has a mass 8.0 kg.
A horizontal force of 100N is exerted on box A.
Let a be the acceleration of the system. Using second law of motion,
Now applying Newton's second law to box B. So,
So, 2.75 N is the force that box A exerts on box B.
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Answer:
x = 0.775m
Explanation:
Conceptual analysis
In the attached figure we see the locations of the charges. We place the charge q₃ at a distance x from the origin. The forces F₂₃ and F₁₃ are attractive forces because the charges have an opposite sign, and these forces must be equal so that the net force on the charge q₃ is zero.
We apply Coulomb's law to calculate the electrical forces on q₃:
(Electric force of q₂ over q₃)
(Electric force of q₁ over q₃)
Known data
q₁ = 15 μC = 15*10⁻⁶ C
q₂ = 6 μC = 6*10⁻⁶ C
Problem development
F₂₃ = F₁₃
(We cancel k and q₃)
q₂(2-x)² = q₁x²
6×10⁻⁶(2-x)² = 15×10⁻⁶(x)² (We cancel 10⁻⁶)
6(2-x)² = 15(x)²
6(4-4x+x²) = 15x²
24 - 24x + 6x² = 15x²
9x² + 24x - 24 = 0
The solution of the quadratic equation is:
x₁ = 0.775m
x₂ = -3.44m
x₁ meets the conditions for the forces to cancel in q₃
x₂ does not meet the conditions because the forces would remain in the same direction and would not cancel
The negative charge q₃ must be placed on x = 0.775 so that the net force is equal to zero.
Answer:
B) the sound source moves towards you at 100 m/sec
Explanation:
The Dopper Effect is a phenomenon that occur when there is relative motion between an observer and a source of a wave. When this situation occurs, there is an apparent shift in frequency of the wave, as observed by the observer.
The apparent frequency observed by the observer is given by
where
f is the original frequency of the wave
f' is the apparent frequency
v is the speed of the wave
is the velocity of the observer (positive if moving towards the source of the wave, negative otherwise)
is the velocity of the source (negative if moving towards from the observer, positive otherwise)
In this problem, we want to find the scenario in which the sound frequency is higher.
We see that in all 4 scenarios, the sound source is moving: this means we have to find the scenario in which the denominator of the equation is smaller.
First of all, we notice the sound source moves towards the observer, is negative, so the denominator is higher: this means that the correct option must be either A or B.
Also, we notice that since is negative, a value larger in magnitude will mean a smaller denominator: therefore, the correct answer will be
B) the sound source moves towards you at 100 m/sec
Since this situation will make the denominator of the formula the smallest possible.