A box of oranges which weighs 81 N is being pushed across a horizontal floor. As

Question

A box of oranges which weighs 81 N is being pushed across a horizontal floor. As it moves, it is slowing at a constant rate of 0.90 m/s each second. The push force has a horizontal component of 20 N and a vertical component of 25 N downward.

Part A:

Calculate the magnitude of the frictional force between the box and floor.

Express your answer using two significant figures.

___________________________ N

Part B

Calculate the magnitude of the upward normal force of the floor on the box of oranges.

Express your answer using two significant figures.

____________________________N

Explanation / Answer

box weight w=81 N

==> mass m=81/9.8 =8.26 kg

accelaration a=0.9 m/sec^2

Fx=20 N and Fy=25 N

A)

frictional force f=uk*N

and N=(mg+Fy)

f=uk*(81+25)

f=uk*(106)

and

Fx=20 N

force along horizontal F=Fx-fs

===>

m*a=20-uk*(106)

m*a=20-uk*(106)

m*0.9=20-uk*(106)

8.26*0.9=20-uk*(106)

uk=(20-8.26*0.9)/106

uk=0.12

now,

frictional froce

f=uk*(106)

=0.12*(106)

=12.72 N

B)

Normal force N=(mg+Fy)

=81+25

=106 N

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