Recent questions in Force, Motion and Energy

Gravitational force
Answered

anniferathonniz8km
2022-05-08

Gravitational force
Answered

tuehanhyd8ml
2022-05-07

(b) Calculate the force on the baby due to Jupiter if it is at its closest to the earth, some $6.29\times {10}^{11}m$ away, showing it to be comparable to that of the father. The mass of Jupiter is about $1.90\times {10}^{27}\text{}kg$. Other objects in the room and the hospital building also exert similar gravitational forces. (Of course, there could be an unknown force acting, but scientists first need to be convinced that there is even an effect, much less that an unknown force causes it.)

Gravitational force
Answered

Ainsley Zimmerman
2022-05-07

Secondary
Answered

2022-05-06

Energy is conventionally measured in Calories as well as in joules. One Calorie in nutrition is 1 kilocalorie, which we define as 1 kcal = 4186 J. Metabolizing 1 gram of fat can release 9.00 kcal.

A student decides to try to lose weight by exercising. She plans to run up and down the stairs in a football stadium as fast as she can and as many times as necessary. Is this in itself a practical way to lose weight?

To evaluate the program, suppose she runs up a flight of 74 steps, each 0.173 m high, in 58.8 s. For simplicity, ignore the energy she uses in coming down (which is small). Assume that a typical efficiency for human muscles is 20.0%. This means that when your body converts 100 J from metabolizing fat, 20 J goes into doing mechanical work (here, climbing stairs). The remainder goes into internal energy. Assume the student's mass is 52.8 kg.

How many times must she run the flight of stairs to lose 1 pound of fat? (1 lb = 0.454 kg)

What is her average power output, in watts and in horsepower, as she is running up the stairs? (1hp = 746 W)

Acceleration Due to Gravity
Answered

ulcerat9jr
2022-05-02

This seems like pretty basic experiment, but I'm having a lot of trouble with it. Basically, I have two timer gates that measure time between two signals, and I drop metal ball between them. This way I'm getting distance traveled, and time. Ball is dropped from right above the first gate to make sure initial velocity is as small as possible (no way to make it 0 with this setup/timer). I'm assuming $v$ initial is $0\frac{m}{s}$. Gates are $1$ meter apart.

Times are pretty consistent, and average result from dropping ball from $1.0$ meters is $0.4003$ seconds.

So now I have $3$ [constant acceleration] equations that I can use to get $g$

1.

${d}_{traveled}={v}_{initial}.t+\frac{1}{2}a{t}^{2}$

$a=\frac{2d}{{t}^{2}}$

$a=\frac{2.1}{(.4003{)}^{2}}$

$a=12.48\frac{m}{{s}^{2}}$

2.

${v}_{f}^{2}={v}_{i}^{2}+2ad$

$a=\frac{{v}_{f}^{2}-{v}_{i}^{2}}{2d}$

${v}_{f}=\frac{distance}{time}=\frac{1.0}{0.4003}=2.5\frac{m}{s}$

$a=\frac{(2.5\frac{m}{s}{)}^{2}}{2.1m}$

$a=3.125\frac{m}{{s}^{2}}$

3.

${v}_{f}={v}_{i}+at$

$a=\frac{{v}_{f}-{v}_{i}}{t}$

$a=\frac{2.5m/s-0}{0.4003s}$

$a=6.25\frac{m}{{s}^{2}}$

I'm getting three different results. And all of them are far from $9.8\frac{m}{{s}^{2}}$ . No idea what I'm doing wrong.

Also, if I would drop that ball from different heights, and plot distance-time graph, how can I get acceleration from that?

Gravitational force
Answered

Jordin Olsen
2022-05-02

Acceleration Due to Gravity
Answered

Araceli Soto
2022-04-30

How do you calculate acceleration due to gravity for objects in 3D space?

My current understanding for the force due to gravity on object $i$ from object $j$ is

${\mathbf{F}}_{g}=({\mathbf{r}}_{j}-{\mathbf{r}}_{i}){m}_{j}{m}_{i}G/|{\mathbf{r}}_{j}-{\mathbf{r}}_{i}{|}^{3}$

where ${\mathbf{r}}_{i}$ and ${\mathbf{r}}_{j}$ are the 3D position vectors of object $i$ and object $j$

Is this right? If not, what is?

Also, should

$|{\mathbf{r}}_{j}-{\mathbf{r}}_{i}{|}^{3}$

be the same as $[({x}_{j}-{x}_{i}{)}^{2}+({y}_{j}-{y}_{i}{)}^{2}+({z}_{j}-{z}_{i}{)}^{2}{]}^{3/2}$ or the vector $[|{x}_{j}-{x}_{i}|,|{y}_{j}-{y}_{i}|,|{z}_{j}-{z}_{i}|]$ cubed?

Acceleration Due to Gravity
Answered

Thaddeus Sanders
2022-04-12

The question is the following:

An object accelerates from rest to $100\phantom{\rule{thinmathspace}{0ex}}\mathrm{k}\mathrm{m}$ per hour in $4.0\phantom{\rule{thinmathspace}{0ex}}\text{seconds}$. What fraction of the acceleration due to gravity is the car's acceleration?

From the question above, I can work out the acceleration (change in velocity over change in time) of the object using the given quantities: initial velocity ($0\phantom{\rule{thinmathspace}{0ex}}\mathrm{k}\mathrm{p}\mathrm{h}$), final velocity ($100\phantom{\rule{thinmathspace}{0ex}}\mathrm{k}\mathrm{p}\mathrm{h}$), and time ($4.0\phantom{\rule{thinmathspace}{0ex}}\mathrm{s}$).

But what does gravitational acceleration have to do with this? Is the answer related to friction created by the downward acceleration due to gravity?

Acceleration Due to Gravity
Answered

llunallenaipg5r
2022-04-12

Could a neutron star have sufficient mass and spin so that the centripetal force acts opposite to gravity to make the effective acceleration due to gravity zero or close to 1g? What would happen to the matter at the surface?

Acceleration Due to Gravity
Answered

Cesar Mcguire
2022-04-12

Modelling the Earth as a symmetric, spherical body (and by using the law of gravitation), we come up with the equation

$w={F}_{g}=\frac{G{m}_{E}m}{{R}_{E}^{2}}$

How do we arrive to the equation to get the acceleration due to gravity at the earth's surface?

$g=\frac{G{M}_{E}}{{R}_{E}^{2}}$

Where:

$G=\text{gravitational constant}=6.67\times {10}^{-11}\text{}\mathrm{N}$

${M}_{E}=\text{mass of Earth}=5.98\times {10}^{24}\text{}\mathrm{k}\mathrm{g}$

${R}_{E}=\text{Earth's radius}=6380\text{}\mathrm{k}\mathrm{m}$

One thing I know of is the fact that we use Newton's second law, but how?

Acceleration Due to Gravity
Answered

Jamir Melendez
2022-04-12

If I project a body at a very large velocity such that it reaches a height h which is comparable to Earth's radius, then how to derive an equation for 'h' in terms of initial velocity 'u' and other constants.

This is where I ended up with this problem

S = u²/2g

But g is variable with height as h approaches R

So dg = GM/(R+dr)² --- this is where I think I might be wrong

Hence dS = u²(R+dr)²/GM

So how do I go ahead?

Acceleration Due to Gravity
Answered

Carina Valenzuela
2022-04-12

It might seem obvious but i can't imagine how is gravitational pull is different from acceleration due to gravity?

Acceleration Due to Gravity
Answered

hard12bb30crg
2022-04-07

In Sean Carroll's Spacetime Geometry, there is the following line on Page No.50 in 2014th edition:

"The acceleration of a charged particle in an electromagnetic field is uniquely defined with respect to inertial frames.The EEP,on the other hand,implies that gravity is inescapable- there is no such thing as a "gravitationally neutral object" with respect to which we can measure the acceleration due to gravity. It follows that the acceleration due to gravity is not something that can be reliably defined,and therefore is of little use"

But, we do measure acceleration due to gravity of earth and moon. So why acceleration due to gravity is not reliably defined? Does this mean we cannot measure the true value of acceleration due to gravity of any massive object?

Gravitational force
Answered

Brooklynn Hubbard
2022-04-07

(a) 20,000 miles

(b) 30,000 miles

(c) 100,000 miles

Gravitational force
Answered

Logan Lamb
2022-04-07

(a) What is the gravitational potential energy of the satellite-Earth system?

(b) What is the magnitude of the gravitational force exerted by the Earth on the satellite?

(c) What force does the satellite exert on the Earth?

Secondary
Answered

Carol Valentine
2022-01-05

A proton with an initial speed of 800,000 m/s is brought to rest by an electric field. a. Did the proton move into a region of higher potential or lower potential? b. What was the potential difference that stopped the proton? c. What was the initial kinetic energy of the proton, in electron volts?

Secondary
Answered

pogonofor9z
2022-01-03

A small block is attached to an ideal spring and is moving in SHM on a horizontal, frictionless surface. The amplitude of the motion is 0.240 m and the period is 3.08 s.

a. What is the acceleration of the block when x = 0.160 m?

Secondary
Answered

socorraob
2022-01-02

A 2.0 kg book is lying on a 0.75-m-high table. You pick it up and place it on a bookshelf 2.3 m above the floor. During this process,

How much work does gravity do on the book?

Secondary
Answered

Lennie Davis
2021-12-22

To throw a discus, the thrower holds it with a fully outstretched arm. Starting from rest, he begins to turn with a constant angular acceleration, releasing the discuss after making one complete revolution. The diameter of the circle in which the discus moves is about 1.8 m. If the thrower takes 1.0 s to complete one revolution, starting from rest, what will be the speed of the discus at release?

Secondary
Answered

Jean Blumer
2021-12-20

A550-N physics student stands on a bathroom scale in an elevator that is supported by a cable. The combined mass of student plus elevator is 850 kg. As the elevator starts moving, the scale reads 450 N.

(a) Find the acceleration of the elevator (magnitude and direction).

(b) What is the acceleration if the scale reads 670 N?

(c) If the scale reads zero, should the student worry? Explain.

(d) What is the tension in the cable in parts (a) and (с)?

When you have to provide correct answers to the questions based on motion equations physics, you must start with the examples that can help you learn more about the theory and see relevant examples. If you find it too challenging, start with the equations that help to determine the force of the motion as you estimate the energy that is being produced. It’s also helpful to compare several lab experiments to see the differences in how the concepts operate. Such an approach will help you to see the example of force and explain it both verbally and with the formulas.