Chapter 5: 2Q (page 206)
Question: A student said, "When the Moon goes around the Earth, there is an inward force due to the Moon and an outward force due to centrifugal force, so the net force on the Moon is zero." Give two or more physics reasons why this is wrong.
Answer
The net force is non-zero.
Over 30 million students worldwide already upgrade their learning with Vaia!
All the tools & learning materials you need for study success - in one app.
Get started for free
An object is moving with constant momentum . What is the rate of change of momentum? What is the net force acting on the object? The object is acted on by three objects in the surroundings. Two of the forces are and . What is the third force?
A block with mass 0.4 kgis connected by a spring of relaxed length 0.15 mto a post at the centre of a low-friction table. You pull the block straight away from the post and release it, and you observe that the period of oscillation is 0.6 s. Next you stretch the spring to a length of 0.28mand give the block an initial speed vperpendicular to the spring, choosing vso that the motion is a circle with the post at the centre. What is this speed?
Anload is suspended as shown in Figure . (a) Calculate the tension in all three wires (that is, the magnitude of the tension force exerted by each of these wires). (b) These wires are made of a material whose value for Young’s modulus is . The diameter of the wires is . What is the strain (fractional stretch) in each wire?
(a) Many communication satellites are placed in a circular orbit around the Earth at a radius where the period (the time to go around the Earth once) is\(24\;{\rm{h}}\). If the satellite is above some point on the equator, it stays above that point as the Earth rotates, so that as viewed from the rotating Earth the satellite appears to be motionless. That is why you see dish antennas pointing at a fixed point in space. Calculate the radius of the orbit of such a "synchronous" satellite. Explain your calculation in detail.
(b) Electromagnetic radiation including light and radio waves travels at a speed of\(3 \times {10^8}\;{\rm{m}}/{\rm{s}}\). If a phone call is routed through a synchronous satellite to someone not very far from you on the ground, what is the minimum delay between saying something and getting a response? Explain. Include in your explanation a diagram of the situation.
(c) Some human-made satellites are placed in "near-Earth" orbit, just high enough to be above almost all of the atmosphere. Calculate how long it takes for such a satellite to go around the Earth once, and explain any approximations you make.
(d) Calculate the orbital speed for a near-Earth orbit, which must be provided by the launch rocket. (The advantages of near-Earth communications satellites include making the signal delay unnoticeable, but with the disadvantage of having to track the satellites actively and having to use many satellites to ensure that at least one is always visible over a particular region.)
(e) When the first two astronauts landed on the Moon, a third astronaut remained in an orbiter in circular orbit near the Moon's surface. During half of every complete orbit, the orbiter was behind the Moon and out of radio contact with the Earth. On each orbit, how long was the time when radio contact was lost?
A Ferris wheel is a vertical, circular amusement ride. Riders sit on seats that swivel to remain horizontal as the wheel turns. The wheel has a radius and rotates at a constant rate, going around once in a time. At the bottom of the ride, what are the magnitude and direction of the force exerted by the seat on a rider of mass ? Include a diagram of the forces on the rider.
What do you think about this solution?
We value your feedback to improve our textbook solutions.
