
#1
Oct2206, 06:52 PM

P: 32

I am attempting 3 questions I have worked them out but to no avail. I wonder if I am on the right track:
1st Question: Starting from rest at the top, a child slides down the water slide at a swimming pool and enters the water at a final speed of 5.00 m/s. At what final speed would the child enter the water if the water slide were twice as high? Ignore friction and resistance from the air and the water lubricating the slide. Here I am using the principal of conservation of mechanical energy that can be rewritten as follows: Vf = Sqrt(Vo^2 + 2g(ho  hf) So I assign a random number (I used 5) to hf and I get: 5.0 m/s = Sqrt(0 + 19.6(Ho  5)) 5 = Sqrt(19.6ho  98) 25 = 19.6ho  98 ho = 6.2755 So since the H is twice what it would be I used 12.551 And get: Vf = Sqrt(Vo^2 + 19.6(12.551  5)) Vf = 12.16 <Wrong....is there somewhere I went wrong??? SECOND QUESTION: A 915kg car starts from rest at the bottom of a drive way and has a speed of 3.00 m/s at a point where the drive way has risen a vertical height of 0.600 m. Friction and the drive force produced by the engine are the only two nonconservative forces present. Friction does 2870 J of work. How much work does the engine do? So I used the Work Energy theorum: Wnc = 1/2m(Vf^2  Vo^2)  mg(ho  hf) Wnc = 457.5(3)^2  8967(6) Wnc = 57919.5 Do you see anything wrong with my math? THIRD QUESTION: The power needed to accelerate a projectile from rest to its launch speed v in a time t is 43.0 W. How much power is needed to accelerate the same projectile from rest to a launch speed of 2 v in a time of t? I am confused by the relationship here....are there any formulas that would apply here? Thanks SO much! Matt 



#2
Oct2206, 07:53 PM

P: 122

For 1. Rearrange Vf to get an expression for ho, you know hf = 0. Then just stick 2*ho back into your original expression to find Vf.




#3
Oct2206, 09:40 PM

P: 32





#4
Oct2306, 07:51 AM

P: 32

3 Questions in regards to WORK AND ENERGY
Does anyone have any ideas for the 2nd and 3rd one?
Thanks! 


Register to reply 
Related Discussions  
Two questions, workkinetic energy related  Introductory Physics Homework  0  
More quick work and energy questions  Introductory Physics Homework  7  
Quick questions on work and energy  Introductory Physics Homework  4  
Two Power / Work / Energy Questions  Introductory Physics Homework  3  
Work & Energy Questions  Introductory Physics Homework  6 