Roller coaster problem involving velocity

  • #1
47
0

Homework Statement



A roller coaster reaches the top of the steepest hill with a speed of 7.0 km/h. It then descends the hill, which is at an average angle of 43° below horizontal and is 46.0 m long. What will its speed be when it reaches the bottom? Assume the coefficient of kinetic Friction is 0.12.

Homework Equations


Ff= U•Fn
F=ma
Vf ^2 - Vo^2 = 2ad

The Attempt at a Solution


Ff=U•Fn
Ff= U•mgcos(43)

F=ma
Mgsin(43) - Umgcos(43) =ma
The mass cancels out here so ,
gsin(43) - Ugcos(43) = a
5.82 = a

Vf= (square roof of>>) 2ad + vo ^2
Vf = (square roof of >> ) 2 • 5.82 • 0.046 + 7.0^2
Vf = 7.04 km/h

The answer should be 83.6 km/h
Where did I go wrong
 

Answers and Replies

  • #2
TSny
Homework Helper
Gold Member
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3,099
5.82 = a
What are the units for this acceleration?
 
  • #3
47
0
What are the units for this acceleration?
I just realized it was m/s^2
Thank you
 

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