# A block starts at rest and slides down a 3 meter long incline plane at 30 degrees in 3 seconds.?

A block starts at rest and slides down a 3 meter long incline plane at 30 degrees in 3 seconds. Calculate the coefficient of kinetic friction between the block and the incline plane. Hint: use kinematics to find the acceleration, then use a force diagram to solve for the coefficient of kinetic friction.

### 2 Answers

- Old Science GuyLv 72 months ago
find a

d = Vi t + 1/2 a t^2

you have t and d and Vi=0

solve for a

then

Fnet = m a

let's take m as 1 kg for convenience

and

Fnet = Fp - Ff = m g sin(angle) - Ff

solve for Ff

then

mu = Ff/Fn = Ff / (m g cos(angle) )

I get about 0.5

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- Anonymous2 months ago
distance = 1/2 * a * time^2

3 m = 1/2 * a * (3 sec)^2, a = 2/3 m/sec^2

if there was no friction, the acceleration of the block would be g * sin 30 = 4.905 m/sec^2 so there is a lot of friction.

Force of gravity acting on the block = m * g * sin 30

Force of friction acting on the block in the opposite direction = m * (4.905 m/sec^2 - 2/3 m/sec^2)

Kinetic coefficient of friction = m * (4.905 m/sec^2 - 2/3 m/sec^2) / m * g * sin 30 = 0.865

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