# Recent content by Natko

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...