Work and Power Homework problem

AI Thread Summary
Tarzan swings from a tree using a 20 m vine at a 45-degree angle, aiming to reach Jane in another tree, with the final angle being 30 degrees. The problem involves calculating Tarzan's speed just before he reaches Jane, utilizing the work-energy theorem and conservation of energy principles. The discussion reveals confusion about how to apply these concepts, particularly regarding the necessary quantities for the energy equation. Participants suggest focusing on initial and final kinetic and potential energy to solve the problem. The overall sentiment reflects a struggle to correctly apply the conservation of energy to find the solution.
Santorican
Messages
10
Reaction score
0
This question, I have absolutely no idea what to do.


Question: Tarzan, in one tree, sights Jane in another tree. He grabs the end of a vine with length 20 m that makes an angle of 45 degrees with the vertical, steps off his tree limb, and swings down and then up to Jane's open arms. When he arrives, his vine makes an angle of 30 degrees with the vertical.

Part A)
Calculate Tarzan's speed just before he reaches Jane. You can ignore air resistance and the mass of the vine.

I figured that I am going to have to use the work energy theorm, W=change in K and then break it down into smaller bits, but there is no mass and I have no idea what work is equal to so I am totally stumped.
 
Physics news on Phys.org
Try using conservation of energy. The vine does not actually do any work on Tarzan.
 
So by using Ue=Uk and breaking it down I can figure out the answer!? That is so beautifully simply!

Thank you
 
Okay so I tried using the conservation of energy Ue=Ke and then broke it down to mgh=(mv^2)/2 and then simplified to find velocity but this is where I am confused.

I tried using V=(2gh)^1/2 and it was wrong.

Then I tried to find the component of gravity at a 30 degree angle with respect to y and used V=(2(sin30g)h)^1/2 and it was wrong.

Then again with respect to x, don't have a clue at this point, V=(2g(cos30)h)^1/2 and it too was wrong.

So right now I am utterly completely lost. Please help :(
 
Well, for conservation of energy you need 4 quantities to set up the equation:
initial kinetic energy and initial potential energy
final kinetic energy and final potential energy
 
Thread 'Variable mass system : water sprayed into a moving container'
Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
I was thinking using 2 purple mattress samples, and taping them together, I do want other ideas though, the main guidelines are; Must have a volume LESS than 1600 cubic centimeters, and CAN'T exceed 25 cm in ANY direction. Must be LESS than 1 kg. NO parachutes. NO glue or Tape can touch the egg. MUST be able to take egg out in less than 1 minute. Grade A large eggs will be used.
Back
Top