A 1,220-N crate is being pushed across a level fioor at a constant spaed by a fo

Question

A 1,220-N crate is being pushed across a level fioor at a constant spaed by a force F of 250 N at an angle of 20.0 below the horizontal, as shown in the figure a below 20.00 (a) What is the coetticient of kinetic triction between the crate and the tor? (Enter your answer to at least three decimal places.) (b) IT the 250-N force is instead pulling the block at an angle of 20.0 above the horizontal, as shown in the figure b, l be the acceleration of the crate? Assume that the coericient of frietion is the same as that found in part (a) m/s Need Help? Read t

Explanation / Answer

a) for the normal force

N = W + F * sin(20 degree)

N = 1220 + 250 * sin(20)

N = 1305 N

let the coefficient of friction is u

F * cos(theta) = u * N

250 * cos(20 degree) = u * 1305

u = 0.18

the coefficient of friction is 0.18

b)

let the acceleration is a

in this case , N = N = W - F * sin(20 degree)

N = 1220 - 250 * sin(20)

N = 1135 N

m * a = F * cos(theta) - u * N

(1220/9.8)* a = 250 * cos(20) - 0.18 * 1135

a = 0.27 m/s^2

the acceleration is 0.27 m/s^2

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