Energy err

Truck brakes can fail if they get too hot. In some mountainous areas, ramps of loose gravel are constructed to stop runaway trucks that have lost their brakes. The combination of a slight upward slope and a large coefficient of friction in the gravel brings the truck safely to a halt. Suppose a gravel ramp slopes upward at 6 deg. and the coefficient of friction is 0.40.

Use work and energy to find the length of a ramp that will stop a 15,000 kg truck that enters the ramp at 35m/s

Delta(kinetic energy)=W(net)

W(friction)= -u_k*m*g*d(distance)
W(gravity)= -m*g*(delta y)

0.5*m*v^2= W(friction) and then you solve for d.. is this right? because i got some really weird answers
 
Find y in terms of d using trig and then do W(Friction) + W(gravity) = KE
 
maybe i screwed up the math..because that didnt work

0.5*m*v^2=(-u_k*m*g*D)-(m*g*D*sin(6))
9187500=-58860d-146344d
9187500=-205204d
d=12.4

and that was still wrong, and i cant see where i messed up in the math
 

The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top