Homework Help Forum: Physics

Posted by Shawna on Wednesday, November 4, 2009 at 2:10pm.

A 3.0 kg breadbox on a frictionless incline of angle еш = 42 вк is connected, by a cord that runs over a pulley, to a light spring of spring constant k = 110 N/m, as shown in the figure. The box is released from rest when the spring is unstretched. Assume that the pulley is massless and frictionless. (a) What is the speed of the box when it has moved 9.0 cm down the incline? (b) How far down the incline from its point of release does the box slide before momentarily stopping, and what are the (c) magnitude and (d) direction (if up the incline then type 1, if down the incline then type 2) of the box's acceleration at the instant the box momentarily stops?

• Physics - Shawna, Wednesday, November 4, 2009 at 2:12pm

  Angle is 42 degrees

  
  

• Physics - bobpursley, Wednesday, November 4, 2009 at 3:17pm

  The sum of energies is a constant. gPE + KE + PEspring=K initially, KE, PEspring is zero. so gPE is k now when it is down the plane .09m, -.09sin42+KE+1/2 k .09^2=0 so you can figure KE. When it stops, then KE is zero, and x*sin42=1/2 k x^2

  
  

• Physics - Shawna, Wednesday, November 4, 2009 at 3:29pm

  Thank you, but how do you obtain the speed of the box?

  
  

• Physics - Shawna, Wednesday, November 4, 2009 at 3:42pm

  K=mv^2 ? And acceleration? Sorry, I am just so confused right now

  
  

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