Register to reply 
Loop on a track 
Share this thread: 
#1
Nov2508, 01:12 PM

P: 7

1. The problem statement, all variables and given/known data
A block of mass 0.640 kg is pushed against a horizontal spring of negligible mass until the spring is compressed a distance x. The force constant of the spring is 450 N/m. When it is released, the block travels along a frictionless, horizontal surface to point B, the bottom of a vertical circular track of radius R = 1.00 m, and continues to move up the track. The speed of the block at the bottom of the track is vB = 14.0 m/s, and the block experiences an average frictional force of 7.00 N while sliding up the track. (a) What is x? (b) What speed do you predict for the block at the top of the track? I've gotten (a) but can not figure out (b). 2. Relevant equations Σ_{nc}=ΔKE + ΔU_{g} + ΔU_{s} 3. The attempt at a solution (a)What is x? Σ_{nc}=ΔKE + ΔU_{g} + ΔU_{s} Σ_{nc}=(1/2)*m*v_{f}^2  (1/2)*m*v_{i}^2 + mgh_{f}  mgh_{i} + (1/2)*k*x_{f}^2  (1/2)*k*x_{i}^2 Σ_{nc}=(1/2)*m*v_{f}^2  (1/2)*k*x_{f}^2 0=(1/2)*0.640*14^2  (1/2)*450*x_{f}^2 x=0.528 This is the one I'm having trouble on (b) What speed do you predict for the block at the top of the track? I'm assuming that the work done by the friction is F*Δr = 7.00 * Π since the displacement is half the loop. I'm also assuming that the height at the top of the loop is 2 meters. Σ_{nc}=ΔKE + ΔU_{g} + ΔU_{s} Σ_{nc}=(1/2)*m*v_{f}^2  (1/2)*m*v_{i}^2 + mgh_{f}  mgh_{i} + (1/2)*k*x_{f}^2  (1/2)*k*x_{i}^2 Σ_{nc}=(1/2)*m*v_{f}^2  mgh_{f}  (1/2)*k*x_{f}^2 7.00*Π=(1/2)*0.640*v_{f}^2  0.640*9.81*2  (1/2)*450*(0.528)^2 v_{f}=12.9 m/s 


Register to reply 
Related Discussions  
Riding a Loop the Loop (velocity at the bottom of the loop)  Introductory Physics Homework  13  
Calculating normal force in a looptheloop situation  Introductory Physics Homework  2  
Block on looptheloop track  Introductory Physics Homework  34  
Work done by mass on a looptheloop track  Introductory Physics Homework  10  
A looptheloop track problem  Introductory Physics Homework  3 