# Force, motion and energy problems and answers

Recent questions in Force, Motion and Energy
vulkanere64t6 2022-05-18

### A 20kg block and a 2kg block are falling with no air resistance. What is the gravitational force on the 20kg block?

Jaiden Bowman 2022-05-18

### How to expand this equation considering acceleration due to gravity into 3D vector space?How can we expand this following equation into 3D vector space? I learned this equation from this answer: Don't heavier objects actually fall faster because they exert their own gravity?The answer shows how we can find time as function of distance (or single dimension) when there's force due to gravity accelerating both pieces of mass as follows:$t=\frac{1}{\sqrt{2G\left({m}_{1}+{m}_{2}\right)}}\left(\sqrt{{r}_{i}{r}_{f}\left({r}_{i}-{r}_{f}\right)}+{r}_{i}^{3/2}{\mathrm{cos}}^{-1}\sqrt{\frac{{r}_{f}}{{r}_{i}}}\right)$Where ${m}_{1}$ and ${m}_{2}$ are the masses of two bodies, ${r}_{i}$ is initial distance from mass to another and ${r}_{f}$ is the final distance from mass to another.If this equation had just the force caused by gravity within it, I could easily divide it into components, and use this equation for each dimension, but as seen, this equation only has masses and distances in it.How can I apply this kind of equation into 3d vector space, ie. get the position as 3d coordinates as function of time when initial position and velocity are known?If this equation cannot be applied in to 3d space, then how could we derive another equation, which applies same kind of relations into 3d vector space? (I checked the answer I linked above, but it goes somewhat above my understanding, as differential equations are used.)

dresu9dnjn 2022-05-18

### Given that the electrical force is so much stronger than gravitational force at atomic levels, why is it that it's the gravitational force between you and the earth that keeps you on the ground rather than the electrical force between you and the earth?

lurtzslikgtgjd 2022-05-17

### A setellite in Earth orbit has a mass of 91 kg and is at an altitude of $2.04×{10}^{6}m$. (Assume that U = 0 as $r\to \mathrm{\infty }$)(a) What is the potential energy of the satellite-Earth system?J(b) What is the magnitude of the gravitational force exerted by the Earth on the satellite?N(c) What force, if any, does the satellite exert on the Earth? (Enter the magnitude of the force, if there is no forN

sembuang711q6 2022-05-17

### Acceleration due to gravity on Coil vs InsulatorConsider I have a coil with a length of $5m$ and made up of copper wire with a diameter of cross-section $d$ and wrapped around an imaginary axis with radius $R$ with mass $M$Now consider an insulator made up of a glass of mass $M$ of $5m$ of diameter $D$If both were taken very high in the atmosphere but not away from the gravity of the earth. Then it is dropped from that point at the same level without providing any external force.My question is that which object will move fasterConductor. ORInsulatorI have been taught that every object of any mass will have same acceleration due to gravity but electromagnetism course taught us that a coil will produce induction and it will slow down or speed up the coil.Which theory is true?

Stoyanovahvsbh 2022-05-15

### Does GR imply a fundamental difference between gravitational and non-gravitational acceleration?1.Does the equivalence principle imply that there is some fundamental difference between acceleration due to gravity and acceleration by other means (because there is no way to 'feel' free fall acceleration for a uniform gravitational field)?2.Does General Relativity allow you to describe the acceleration due to gravity without Newton's second law (because every other source of 'push or pull' outside the nucleus involves the electromagnetic field)?3.Is the acceleration due to gravity a result of changes in time dilation/length contraction as opposed to an actual push or pull?\

Jayla Faulkner 2022-05-14

### An electron and a positron are separated by distance r. Findthe ratio of the gravitational force to the electric force betweenthem. From the result, what can you conclude concerning theforces acting between particles detected in a bubble chamber?(Should gravitational interactions be considered?)

vulkanere64t6 2022-05-14

### How is the gravitational force between two point masses affected when they are dipped in water keeping the seperation between them the same?

Dominick Blanchard 2022-05-14

### (a) Calculate the gravitational force exerted on a 5.00 kg baby by a 90 kg father 0.200 m away at birth (assisting so he is close).(b) Calculate the force on the baby due to Jupiter if it is at its closest to the earth, some $6.29×{10}^{11}m$ away, showing it to be comparable to that of the father. The mass of Jupiter is about . Other objects in the room and the hospital building also exert similar gravitational forces.

Jayden Mckay 2022-05-13

### The only known force a planet exerts on Earth is gravitational. (a) Calculate the magnitude of the gravitational force exerted on a 4.20 kg baby by a 100 kg father 0.200 m away at birth (he is assisting, so he is close to the child). (b) Calculate the magnitude of the force on the baby due to Jupiter if it is at its closest distance to Earth, some away. How does the force of Jupiter on the baby compare to the force of the father on the baby? 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.)

Reese Estes 2022-05-13

### Two balls have their centers 2.0 m apart. One ball has a mass of 8.0 kg. The other has a mass of 6.0 kg. What is the gravitational force between them?

Elle Weber 2022-05-13

### What is the electric potential at the point indicated with the dot in the figure? Express your answer to two significant figures and include the appropriate units.photo

mars6svhym 2022-05-13

### What is the jerk due to gravity with ascent? Acceleration is defined as the rate of change of velocity with time. Jerk is defined as the rate of change of acceleration with time. What is the jerk due to gravity with ascent?

ga2t1a2dan1oj 2022-05-13

### When an object, say a ball, is attracted by the black hole it gets acceleration due to gravity. Suppose light is moving towards the black hole vertical to it... then does it gain acceleration due to gravity? If yes then won't be the speed of light increase and get violated?

Jaeden Weaver 2022-05-13

### Why do we use gravitational force in earth by relating just the mass of an object with the acceleration produced by the gravitational field:${F}_{g}=m\cdot \stackrel{\to }{g}$And when we're dealing with planets, we use a relation defined by the masses of two planets, distance squared and gravitational constant:${F}_{g}=G\cdot \frac{{M}_{1}\cdot {M}_{2}}{{d}^{2}}$I really don't get why we use just the first relation here on earth, because we're dealing with a interction between two objects... It's because our mass is irrelevant??

Zyrill Maravilla 2022-05-13

### Determine the speed a2500-kg pick-up truck should attain for it to have (a) the same momentum as a 20,000-kg bus travelling at 90-kph (b) the same kinetic energy as a 1800-kg car travelling at 100-kph

Matilda Webb 2022-05-10

### Is acceleration due to gravity constant?I was taught in school that acceleration due to gravity is constant. But recently, when I checked Physics textbook, I noted that$F=\frac{G{m}_{1}{m}_{2}}{{r}^{2}}.$So, as the body falls down, $r$ must be changing, so should acceleration due to gravity.

fetsBedscurce4why1 2022-05-10

### Why do we integrate along the whole length while finding the gravitational force between a object of mass (m) and a rod of length L and mass M? Can't we simply use $F=\frac{GmM}{{r}^{2}}\phantom{\rule{thinmathspace}{0ex}}?$?

sg101cp6vv 2022-05-10

### Two objects are attracted to each other with 36 N of gravitational force. What would the force between them be if the distance between them were doubled?

syaoronsangelhwc17 2022-05-10