Theory questions about Newton's Laws and Gravitation

In summary, the first problem involves two planets circling a star, with the second planet having an orbit 4 times the size of the first. The second planet will take 4 times longer to revolve once. The second problem involves two blocks connected by a massless cord on a frictionless surface. The tension of the cord can be determined by finding the acceleration of the system and applying it to the tension between the blocks. In the case of no friction, the smaller force can be treated as an outsized friction on the second block.
  • #1
ohsolost
2
0
I'm trying to figure out these two problems and I'm so lost!

1. Two planets are circling a star. The second planet has an orbit 4 times the size of the first planet. By the time the first planet revolves once, how many times the second one will?

My solution: the formula is T=2PiR/v... so wouldn't the second planet take 4 times as long?

2. Two blocks, which both have the mass of 3kg, are lying on a frictionless surface and are connected by a massless cord. One block is being pulled to the left with a force of 2.5N, and the other block is being pulled to the right with a force of 11.5N. What is the tension of the cord?

My solution: Since there's no friction, don't I just subtract the two forces?
 
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  • #2
What's the relationship between the tangential speed v, and the radius of the circular motion under the influence of the gravitational force? They depend on each-other, the answer to question #1 is not trivial.
 
  • #3
Welcome to PF.

For 2, you need to determine the acceleration that the system is subjected to. Then you can apply that to the tension between the blocks
 
  • #4
Thanks.Doesn't something weird happen to acceleration when there's no friction?
 
  • #5
ohsolost said:
Thanks.Doesn't something weird happen to acceleration when there's no friction?

Weird. Like no resistance to motion weird?

Then yes. Frictionless only seems to happen in physics homework problems.

For 2) you could treat the smaller force as though it were out-sized friction on the second block only.
 

1. What are Newton's three laws of motion?

Newton's first law states that an object at rest will remain at rest and an object in motion will remain in motion at a constant velocity, unless acted upon by an external force. Newton's second law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Newton's third law states that for every action, there is an equal and opposite reaction.

2. How do Newton's laws of motion apply to everyday life?

Newton's laws of motion can be observed in everyday life in many ways. For example, Newton's first law can be seen when a car comes to a stop at a red light, and Newton's second law can be seen when a person pushes a shopping cart and it accelerates in the direction of the force applied.

3. What is the law of universal gravitation?

The law of universal gravitation states that every object in the universe attracts every other object with a force that is directly proportional to their masses and inversely proportional to the square of the distance between them.

4. How did Newton's discovery of gravity change our understanding of the universe?

Newton's discovery of gravity provided a mathematical explanation for the motions of planets and other celestial bodies, leading to a better understanding of the laws that govern the universe. It also paved the way for future advancements in physics and astronomy.

5. How does the force of gravity affect objects on Earth?

The force of gravity on Earth is responsible for keeping objects in orbit, such as the Moon around the Earth and the Earth around the Sun. It also causes objects to fall towards the ground, giving weight to objects and keeping them on the surface of the Earth.

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