# How to use the coefficient of kinetic friction?

• Hannah
In summary: Nope, you are close but wrong. Your question mentions that there is a horizontal lower section before elevation to an upper section. So, for the horizontal section it should be ##kx = ma## but we don't know the length of the horizontal section. So how else can we do it?I think part b) should be easy now that we know what the normal force is. Draw a graph and label it with the forces and their associated values.I think part b) should be easy now that we know what the normal force is. Draw a graph and label it with the forces and their associated values.The child launches a car using a spring loaded launcher. The launcher has a spring that must be compressed by 2
so just one thing since i used conservation of energy my system would have to isolated so would i have to include the Earth as my system or just track+spring+car since its isolated until it reaches the top part of the track?

Hannah said:
so just one thing since i used conservation of energy my system would have to isolated so would i have to include the Earth as my system or just track+spring+car since its isolated until it reaches the top part of the track?
You need to include the Earth, and you do that by considering the change in gravitational PE.

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