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1. Energy and basic math (proportionality)

Changed my previous post. Thanks!
2. Energy and basic math (proportionality)

v12 = ((1/2)v0)2 If I let v0 = 1, then v1 = sqrt(1/2), which equals 0.71 :)
3. Energy and basic math (proportionality)

Well, 1/2 squared is 0.25, and 12 halved is 0.5. How do I get to 0.71?
4. Energy and basic math (proportionality)

Homework Statement A person running in a race has to pick up a mass equal to her own mass. Assuming she can still do the same amount of work, her speed will be changed by a factor of a. 0.25 b. 0.50 c. 0.71 d. 1 e. 2 Homework Equations E=1/2mv2 The Attempt at a Solution Since m is...
5. Calculating Distance Given Work and Forces

Homework Statement A farmhand does 972 J of work pulling an empty hay wagon along level ground with a force of 310 N [23 degrees below the horizontal]. A frictional force of 280 N opposes the motion. The distance the wagon travels is a. 0.39 m b. 1.7 m c. 3.4 m d. 32 m e. 1.8 x 102 m Homework...
6. Sum of Infinite Series

Ok, thank you for your replies. Does this mean that 1+2+3+4+5+...=−1/12 is actually just a mathematical hoax, that the youtuber had no legitimate intention in his "educational" video, even though this equation (or whatever it's called) is used in many physics textbooks and theories (e.g. string...
7. Sum of Infinite Series

I'm not sure which category this post actually belongs to, or if the title of this post is even accurate. I guessed Calculus was the closest one. I watched this video on the web after a professor told me this mathematical phenomenon (http://www.youtube.com/watch?v=w-I6XTVZXww‎). It asserts...
8. Three girls pull a sled. Determine the acceleration.

Thanks for the tips. I'll try: Fy=10sin30-10sin40 =-1.428 N Fx= 10cos30+10cos40-2 =14.32 N √(Fy2+Fx2)=14.39 N Θ=tan-1(Fy/Fx) =5.67 a=F/m =1.439 m/s2 [5.67 down of left] Is that correct, or did I mess up somewhere? What does the question mean by "instantaneous?" I know what...
9. Three girls pull a sled. Determine the acceleration.

Homework Statement Two girls pull a sled across a field of snow, as shown in the diagram. A third girl pulls backward with a 2.0 N force. If the mass of the sled is 10 kg, determine its instantaneous acceleration. Homework Equations F=ma The Attempt at a Solution Sorry, I'm stumped.
10. Football Vector Motion Problem

Does this look better? Sorry, it's flipped on PF even though I rotated it on my computer.
11. Football Vector Motion Problem

Homework Statement A quarterback is running across the field, parallel to the line of scrimmage, at a constant speed of 2.5m/s, when he spots an open, stationary receiver straight downfield from him (ie, in a line parallel to the sidelines). If he can throw the football at a speed of 8.0m/s...
12. Find the displacement in a word problem

Whoops, forgot to convert km/h/s to km/h/h. I got the answer now :)
13. Find the displacement in a word problem

Homework Statement A car is slowing down at a rate of 20 km/h/s. How far does it travel if its original velocity is 50 km/h and its final velocity is 5.0 m/s? Homework Equations vf2 = v02 + 2aΔx The Attempt at a Solution vf2 = v02 + 2aΔx Δx = (vf2 - v02) / 2a = (182-502) /...
14. Word Problem with Kinematics Equation

Homework Statement An object thrown up from a cliff 10 m/s reaches a velocity of 20 m/s [down] as it lands. If acceleration due to gravity is 9.8 m/s2, what is the object's displacement? How long did it take for the object to land from the time it was thrown? Homework Equations I'm not...
15. Average Speed vs. Instantaneous Speed

Homework Statement A book falls off a shelf and lands on the floor. Which is greater, the book's average speed or its instantaneous speed right before it lands? Homework Equations v = d/t The Attempt at a Solution I think its the instantaneous speed because the book accelerates...
16. Polyatomic ions and their charge

I still don't get how SeO4 acquires a charge of 2-. I don't understand the diagram above either. Please explain in more plain language.
17. Can irrational numbers exist on the numberline?

This is like The arrow paradox; you can't reach the point on the line as you'd have to go through infinity points in fieri.
18. Cheap Piezoelectric Generator

I believe some of those shoe companies use piezoelectric materials. I'll have to look into that.
19. Movement at Absolute Zero

Is it possible for motion to exist at 0 Kelvin?
20. Can magnets defy the law of energy conservation?

But the kinetic energy from two magnets slamming together is much greater than that required to pull it apart, if done properly, no? Can't magnets demagnetize after many uses? If not, how do they ever demagnetize?
21. Cheap Piezoelectric Generator

With a budget of less than \$100, does anyone have an idea on how to make a cheap piezoelectric generator using materials found at home? (aluminum foil, wire, battery, and a silicon swim cap maybe?) I plan to modify this generator to then integrate it inside a bike tire so that whenever I ride...
22. Can magnets defy the law of energy conservation?

Okay, thank you all for answering. :smile: To clarify, if the magnet has potential energy, when does it lose its potential energy? Maybe when you use the magnet many many times over and over? At that point, will the magnet no longer be magnetic since all of its potential energy has been...
23. Can magnets defy the law of energy conservation?

I'm pretty sure it cannot, but if I put a common bar magnet close to another magnet, they will move towards each other. I don't have much of a background in physics, but it seems to me that the kinetic energy is coming out of...nowhere. I can repeat this experiment as many times as I like but...
24. Confused with the Archimedes' Principle

1. The gravitational force on the bowling ball is greater than the buoyant force and the gravitational force on the rubber ball is less than the buoyant force. Gravity and Buoyant Force work together to conclude whether an object sinks/floats (buoyancy). So the bowling ball has more buoyant...
25. Confused with the Archimedes' Principle

Shouldn't it be the opposite way around? Since the rubber ball is displacing less water but is buoyed more, and the bowling ball is displacing more water but has no buoyant force acting upon it. Also, the two balls start off submerged in the water, so they displace the same volume of water.
26. Confused with the Archimedes' Principle

Archimedes' Principle states: "Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object." If this is true, why then, when you take a bowling ball and submerge it in water, and take a rubber ball of the same size and...
27. Algebraic Expression

So what would the algebraic expression to find the nth term be?
28. Algebraic Expression

That's what I want to find out. It does not necessarily have to be multiplication only. In words it would be: current term value = the previous term's value multiplied by the current term number, and change poles if the current term number is even; the first term value is -15.
29. Algebraic Expression

Homework Statement In this pattern, what is the algebraic expression for the term t? -15, 30, 90, -360 Homework Equations t= term number The Attempt at a Solution no idea
30. How photon entanglement works?

Can you explain how photons can get entangled by SPDC, as well as the CHSH inequality? I cannot understand the Wikipedia explanation.