Finding normal force from kinetic and potential energies

[lsu777]

A 69.2-kg skier encounters a dip in the snow's surface that has a circular cross section with radius of curvature of r = 13.2 m. If the skier's speed at point A in the figure below is 8.13 m/s, what is the normal force exerted by the snow on the skier at point B?

http://educog.com/res/prenhall/walker/Physics_3E/Chap08/graphics/walk0850.gif"

As shown, h = 1.63 m. Ignore frictional forces.




ok so we are given:
mass=69.2kg
radius=13.2m
Velocity1=8.13 m/s
Change in Y=1.63m
gravity=9.81m/s^2

we know KE1 + PE1=KE2 + PE2

with potential energy2= O


ok so first thing I did was try and find velocity2 with the formula

so 1/2*m*v1^2 + 0= 1/2*m*V2^2 + m*g*Y

so V2=sqrt(V1^2 - 2*G*Y)

I got V2=5.84092


Then I did sum of Forces Y=(normal force - m*g)= mass * Arad


Arad= V2^2/R

so normal force=(mass*(V2^2/R))+m*g

so normal force = 709.473 N



can somebody smarter then me please check this. I think I got it wrong the first time because of math error. ****ing lon-capa sucks and doesn't give you any info. I have one more shot to get it right.

 

[ideasrule]

I can't see the diagram without a username and password. Is B lower than A, or higher? Is v1 the speed at A, or B? Make sure everything is consistent.

 

[lsu777]

I can't see the diagram without a username and password. Is B lower than A, or higher? Is v1 the speed at A, or B? Make sure everything is consistent.

A is original heigth, B is the bottom of the circle, below A.

V1= Velocity at A


picture was attached.

 

[ideasrule]

so 1/2*m*v1^2 + 0= 1/2*m*V2^2 + m*g*Y

so V2=sqrt(V1^2 - 2*G*Y)

I got V2=5.84092

Is v1 the speed at A, or B? Is Y the y coordinate at A, or B? Your method is correct, but you have a sign issue. (One way to see that you made a mistake is to note that V2 is smaller than the initial speed, which doesn't make sense.)

 

[lsu777]

Is v1 the speed at A, or B? Is Y the y coordinate at A, or B? Your method is correct, but you have a sign issue. (One way to see that you made a mistake is to note that V2 is smaller than the initial speed, which doesn't make sense.)

v1 is speed at A, Y is the height at B to the level of A. can you tell me where I made a mistake on my signs?

 

[ideasrule]

If your height at A is 0, your height at B should be negative, not positive.