Physics, 30.03.2020 18:53 kelseatuttleni

A 5.0-kg crate is resting on a horizontal plank. The coefficient of static friction is 0.50 and the coefficient of kinetic friction is 0.40. What is the force of friction after one end of the plank is raised so the plank makes an angle of 30 with the horizontal?

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Answer from: sanchez7489

The force of friction after one end of the plank is raised so the plank makes an angle is 21.2 N.

The given parameters;

mass of the crate, m = 5 kgcoefficient of static friction, $\mu_s$ = 0.5coefficient of kinetic friction, $\mu_k$ = 0.40angle of inclination, θ = 30⁰

The normal force on the crate is calculated as follows;

$F_n = mg \times cos \theta\\\\F_n = 5 \times 9.8 \times cos(30)\\\\F_n = 42.43 \ N$

The force of friction after one end of the plank is raised so the plank makes an angle is calculated as follows;

$F_f = \mu_s F_n\\\\F_f = 0.5 \times 42.34\\\\F_f = 21.2 \ N$

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Answer from: bellamore

The mass of the crate is 5kg.

We know that the force of friction can be obtained by:

F = N*k

where k is the coefficient of friction, where we use the static one if the object is at rest, and the kinetic one if the object os moving. N is the normal force

If we tilt the base making an angle of 30° with the horizontal, now the normal force against the plank will be equal to the fraction of the weight in the direction normal to the surface of the plank.

Knowing that the angle is 30°, then the fraction of the weight that pushes against the normal is Cos(30°)*W = cos(30°)*5kg*9.8m/s^2 = 42.4N

The fraction of the force in the parallel direction to the plank (the force that would accelerate the crate downwards) is:

F = sin(30°)*5k*9,8m/s = 24.5N

now, the statical friction force is:

Fs = 42.4N*0.5 = 21.2N

The statical force is less than the 24.5N, so the crate will move downwards, then the force that acts on the crate is the kinetic force of friction:

Fk = 42.4N*0.4 = 16.96N

Then, the total force that acts on the crate is:

total force = F - Fk = 24.5N - 16.69N = 7.54N and the direction of this force points downside along the parallel direction of the plank.

Answer from: Quest

the first step is making objective observations.

they have to be based on a certain event and can be confirmed by others if it is right or not.

Answer from: Quest

does anyone know or what?

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