I have a wooden car sliding down a ramp, it weighs 3kg. The section of the ramp

Question

I have a wooden car sliding down a ramp, it weighs 3kg. The section of the ramp we will be looking at is split into two parts. The first part begins at Point 1 and ends at Point 2. The second part begins at Point 2 and ends at Point 3. Point 1 is 10 meters above the ground and Point 2 is 3 meters above the ground. There is no friction between Points 1 and 2, but there is friction between Points 2 & 3, enough where the car comes to a full stop exactly at Point 3. At Point 1, the car already has a kinetic energy of 50 J. The questions I have are:

&, At Point 2, what's the speed of the car, & what's the magnitude of the frictional force?

Explanation / Answer

At point 1 energy is 50J

at point 2 speed of car wil be

Apply law of conservation of energy 50+mgh=1/2mv^2

V=13.1m/s as h wil be 7m

Velocity at point 2 wil be 13.1m/s

Between 2 and 3

u=13.1m/s,v=0

Apply work energy theorm

Work done by force=change in K.E

0-1/2mu^2=f×s

-1/2×3×13.1×13.1=f×s

-255.75=f×s

Distance covered or ttime to come stop should be given only then we can cal force of friction

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