A 1200 N crate is being pushed across a level floor at a constant speed by a for

Question

A 1200 N crate is being pushed across a level floor at a constant speed by a force Frightarrow of 700 N at an angle of 20.0degree below the horizontal, as shown in Figure P4.37a. Figure P4.37 0.457 is the coefficient of kinetic friction between the crate and the floor? If the 700 N force is instead pulling the block at an angle of 20.0degree above the horizontal as shown in Figure P4.37b, what will be the acceleration of the crate? Assume that the coefficient of friction is the same as that found in (a). ____________ m/s2

Explanation / Answer

The crate moves with constant velocity

N-W-Fsin20=0

where N is the normal reaction

N=1200+700sin20, N=1439.4 N

in X direction

Fcos20-f=0

where f is the frictional force

f=700cos20 =657.8 N

KINETIC FRICTION COEFFICIENT =f/N =657.8/1439.4

=0.457

b)

in Y direction

Fsin20+N-W=0

N=1200-700sin20 =960.6 N

f=uk*N=0.457*960.6 =440 N

m=W/g =1200/9.8 =122.45 kg

ax=(Fco20-f)/m

ax=700cos20-440/122.45

ax=1.784 m/s^2

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