1
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1answer
18 views

Sound and decibels at distance

If I have an object that is 53 decibels at x distance, how many decibels would y objects be at the same distance x, assuming they all created 53 decibels.
1
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3answers
38 views

By how much should the distance from the source be increased to reduce the surface illuminance to 30 lumens?

This is my problem and I have no idea how to solve it: The illuminance of a surface varies inversely with the square of its distance from the light source. If the illuminance of a surface is 120 ...
1
vote
1answer
69 views

How to prove that something is finite

I'm given a physical model of something. Say it's a radius of a planet: $$R=\pi\left(\frac{n}{2\pi G}\right)^{1/2}$$ where $G$ is the universal gravitational constant, n - "positive constant" If I ...
1
vote
3answers
96 views

Moments at which moving points on a circle coincide

Points A $(0,1)$ and B $(1,0)$ start moving along the circumference of a unit circle with center $(0,0)$ in the same, positive (that is, counterclockwise) direction. Every minute, points A and B ...
0
votes
4answers
75 views

Multiple choice question on rates of change (or so I thought)

If I were to find the resistance of the component (see image below), I would either find the equation of the curve and use differentiation or I'd draw a tangent at $V_2$ and then find the reciprocal ...
0
votes
0answers
29 views

Don't understand how this answer is arrived at; dynamic power

According to my notes the fomula for dynmaic energy is $\frac{1}{2}capacitive load \times voltage^2$ and formula for dynamic power is $\frac{1}{2}capaxitive load \times voltage^2 \times switching ...
0
votes
1answer
36 views

Need help deriving an expression for average acceleration in terms of displacement and time

I'm having trouble with this math problem. Here's what the questions is asking: Derive an expression for the average acceleration of the cart in terms of displacement and time of travel. Write ...
1
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2answers
77 views

Square Root Yields Different Result After Unit Conversion [duplicate]

This is boggling my mind. The square root of 100 seconds is 10 seconds The square root of ...
0
votes
0answers
22 views

Closed form for 3j-symbol ratio

I am working on the spherical harmonic decomposition of cosmic microwave background maps, therefore I often deal with functions that are proportional to Wigner 3J symbols/Clebsch Gordan coefficients. ...
0
votes
2answers
46 views

Re-arranging variables

In physics, you can say that: $T-m_2 g = m_2 a$ And that $ m_1 g - T = m_1 a$ So this, when combined, should equal: $a = \frac{m_1}{m_1 + m_2} \cdot g$ How do they arrive at that conclusion? I ...
1
vote
1answer
98 views

Acceleration Vector of a car making a turn without a change in speed

Acceleration Vector (2D) Vector = (Magnitude, Direction) I am trying to calculate the acceleration vector acting on a car moving at a constant speed but changing direction. Example: A car is ...
1
vote
1answer
48 views

Relative horizontal velocity and Origin question

Question: A police boat is chasing a boat with criminals along a straight river by moving against the stream. The speed of the river stream is 3 miles per hour, the speed of the boat with ...
0
votes
1answer
191 views

How to rearrange this equation to find the value of $L$

This question has been difficult for me to answer for awhile. If anyone could help that would be great. The period (the time for one complete swing back and forth) $p$, in seconds of a pendulum is ...
1
vote
1answer
180 views

Determining the minimum angle of a baseball trajectory to get a home run

This is a homework question: The skydome in Toronto has a center field fence that is 10 feet high and 400 feet from home plate. A ball is hit 3 feet above the ground with an initial velocity of ...
2
votes
0answers
41 views

Making a quantity dimensionless

OK, here's another that might be simpler than it looks but I am about ready to give up. Given the following: $$U_\mathrm{eff}(r) = - \frac{k}{r}+ \frac{L^2}{2mr^2}$$ $$\frac{U_\mathrm{eff}}{U_0} = ...
0
votes
2answers
78 views

calculate velocity using parametric functions

if i have the following parametric functions where time is m/s : x = 8 t y = -5 t2 + 6 t and i want to find the initial velocity can i do the following: ...
1
vote
1answer
262 views

Find the position equation from this velocity equation

Find the position equation from this velocity equation $$\displaystyle \frac{dr}{dt} = v_{t}\sqrt{1-e^{-v_{t}t}},$$ where $t$= time and $v_t$= constant I'm wondering if there's a way to solve this ...
0
votes
2answers
159 views

Deriving the Kinematic equation without time? $x = (v^2 - v_0^2)/2a + x_0$

Ok so this is a short question (maybe a little bit more about my inability to do math). I need to derive $x = \frac{v^2 - v_0^2}{2a} + x_0$ from the position function $ = v_0t + \frac{1}{2}at^2 + ...
0
votes
2answers
72 views

Find the average velocity

If a ball is thrown in the air with a velocity $34$ ft/s, its height in feet $t$ seconds later is given by $$ y = 34 t − 16 t^2 .$$ Find the average velocity for the time period beginning when ...
0
votes
2answers
59 views

Gravity beetween planet Earth and another object

The Earth is pulling on an object with gravity given by the formula $F=\frac{k}{r^2}$, $r$ is the distance from the object to the center of the Earth and $k$ is a konstant. If the object is such that ...
0
votes
1answer
937 views

What is the greatest speed he can reach with an acceleration of 5.00 g before blacking out?

A jet fighter pilot wishes to accelerate from rest at $5.00$ G to reach Mach-3 (three times the speed of sound) as quickly as possible. Experimental tests reveal that he will black out if this ...
2
votes
2answers
146 views

Finding the cross sectional area given fuel efficiency.

Your car's fuel efficiency is 35 miles per gallon. Assume that your car's fuel pump pulls fuel out of the fuel tank at a constant rate through a tube. If the speed of the fuel through the tube is ...
1
vote
2answers
1k views

How do I find the mass of a sphere using proportionality?

A steel sphere 3.0 cm in diameter has a mass of 0.11 kg. What is the mass of a steel sphere 5.0 cm in diameter? I know that $m= DV$ where D is density and V is Volume. I am assuming that both spheres ...
1
vote
0answers
718 views

Determine the magnitude of the resultant

The two structural members, one of which is in tension and the other in compression, exert the indicated forces on joint O. Determine the magnitude R of the resultant R of the two forces and the angle ...
4
votes
2answers
136 views

Solving an equation arising from method of image charges

I'm currently studying electrodynamics where the following equation arose: $0 = \frac{q}{\sqrt{R^2 + d^2 - 2Rd\cos\theta}} + \frac{q_p}{\sqrt{R^2 + d_p^2 - 2Rd_p\cos\theta}}$ where I need to solve ...
1
vote
1answer
216 views

Higher Derivatives of trigonometric functions

The position of a particle is given by $s = 5 \cos (2t+ (\pi/4))$ at time $t$ . What are the maximum values of the displacement,the velocity,and the acceleration? The answers are displacement: $5$ ...
0
votes
3answers
53 views

How to isolate $v_m$?

Note: I am not asking anything pertaining to the physics of this question; only the mathematics. The physics is just given as a context to the problem for those interested, as opposed to simply saying ...
2
votes
2answers
143 views

Faulty velocity question?

If a ball is thrown vertically upward with a velocity of $160 \text{ ft/s}$, then its height after t seconds is $s = 160t − 16t^2$. a) What is the velocity of the ball when it is $384 \text{ ...
0
votes
1answer
47 views

Corroboration Of Simple Algebra For A Physics Lab

I have a few equations that I need to solve for a specific variable, and I am wondering if anyone would care to look them over. The first equation is deriving Kepler's equation of orbital period, and ...
0
votes
2answers
408 views

Can somebody help and explain me with angular and linear Velocity textproblems?

So we got this as homework today, and I just don't understand it; how to start or how to do it. Explanations and/or setups would be great :) A wheel with ...
2
votes
2answers
143 views

How to calculate the mass of a layer of an atmosphere?

In a problem I'm working on, I need to derive what fraction of molecules in the Earth's atmosphere are found in the troposphere (the bottom layer extending from the surface to approx. 12 km). I have ...
0
votes
1answer
138 views

Parabolas and projectiles

Given $2$ points, $A$ and $B$, if I am in $A$ and I have an inclination angle $c$, with how many velocity do I need to shoot a projectile to hit $B$ ? My problem is, how do I setup this data in an ...
2
votes
1answer
661 views

How to simultaneously solving trig equations?

I was doing some math work, and have to solve two trig equations simultaneously, but have no idea how to approach this, can anyone help, just need to be pointed in the right direction. I have to ...
0
votes
1answer
27 views

Basic expression mangling question

I am looking at the solution of a physics/statistics hybrid exercise, and I can't figure out how one expression step took place. I have that $${dx \over dt} = gt$$ $$T = \sqrt{2h \over g}$$ where ...
2
votes
4answers
334 views

Trying to find angle at which projectile was fired.

So let's say I have a parabolic function that describes the displacement of some projectile without air resistance. Let's say it's $$y=-4.9x^2+V_0x.$$ I want to know at what angle the projectile ...
1
vote
1answer
57 views

How to define Mach Subsonic by the Mach Supersonic?

I read the book Mechanic of fluids shames and I find this relationship: $$\frac{1+kM_1^2}{1+kM_2^2} =\frac{M_1}{M_2} \left ( \frac{1+\dfrac{(k-1)}{2}M_1^2}{1+\dfrac{(k-1)}{2}M_2^2} \right )^{0.5}$$ ...
1
vote
1answer
644 views

Using Parametric Equations to Define the Position of an Object in Motion

What is the intuition behind the equations for the parametric equation applications below? Rather than memorize the formulas for a quiz i'd like to gain a deep understanding of them.
1
vote
1answer
87 views

The Law of Sines and a second forces magnitude

How do you solve for the second forces magnitude? The 17' and 30' threw me off.
1
vote
1answer
367 views

Simplifying equation using algebraic manipulations

I am trying to calculate the input impedance of a multiple feedback low pass filter. What I need is the simplest symbolic expression so that later I fill in the values and get the impedence itself: ...
0
votes
2answers
124 views

Solving barometric formulae for height

I am wanting to find the height in the barometric equations below. Could anyone solve this? Equation 1: $$ {P}=P_b \cdot \left[\frac{T_b}{T_b + L_b\cdot(h-h_b)}\right]^{\textstyle \frac{g_0 \cdot ...
1
vote
3answers
2k views

How can I calculate the time two people will meet if they are paddling towards each other on a lake?

Here's the question I'm having trouble with. Ken and Kara are 30 miles apart on a calm lake paddling towards each other. Ken paddles at 4 mph, while Kara paddles at 7 mph. HOw long will it take them ...
0
votes
1answer
192 views

Solution for following trigonometric equation?

I have the following trigonometric equation in $\theta$: $$0=G_{\omega}(1/r^2)({\csc^2}\theta){(r\cos\theta-x)}^2+(\cot\theta)(r\cos\theta-x)+r\sin\theta-y.$$ Is there an analytical solution for ...
2
votes
3answers
112 views

Distance and time

So basically I have a said distance. There is one object moving at said speed from one side to the other(lets call it A to B), and another object moving at a different speed(faster speed) from the ...
5
votes
3answers
236 views

Physics: Uniform Motion

Ok so I have this homework problem. I dont want to give out the information because i want to put in the values myself, but basically I have one object moving at said speed. Said time later, another ...
1
vote
4answers
458 views

How to solve for an unknown in two different denominators?

How to solve for an unknown in two different denominators? In this equation: $$F = \frac{GMm_3}{r_2} - \frac{Gmm_3}{d-r_2}.$$ Everything is given except for $r_2$. How do I solve for $r_2$? Is it ...
1
vote
3answers
220 views

How long would it take for light to go through a human eyeball and back to the other side

I couldn't find any TAGS that fit my question... I don't know if I'm doing this correctly. I want to know how long a "twinkling of an eye" would be. A twinkling of an eye is the time it takes from ...
2
votes
4answers
1k views

Calculating acceleration based on a starting and ending distance

I have been trying to figure this problem out and just can't. The answer is supposed to be (A): 1.0 m/s/s. Can anyone tell me how they got that answer? I thought this problem was based on the ...