4.4 Friction and inclines

A 10-N book is being pushed right on a table with a force of 2 N at a constant speed. Label all 4 forces.

c

d

e

f

-4 N

-10 N

0 N

2 N

-2 N

10 N

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NGSS.HS-PS2-1

A box is being pushed right across the floor.

Label each force vector with the correct variable if the box is moving.

b

c

d

e

Fn

Fk

Fsmax

Fg

Fa

Answer explanation

If the box is moving, the friction left must be kinetic. Normal force is perpendicular to the surface.

Tags

NGSS.HS-PS2-1

The coefficient of friction changes between two items when ​ (a)   change(s).

• materials of surfaces
• weight
• surface area
• materials and weight
• normal force

The maximum static friction is usually (a)   kinetic friction.​

• greater than
• less than
• equal to
• unrelated to
• 0 compared to

Answer explanation

It usually takes more force to get it unstuck so static is larger than kinetic.

You push a box that weighs 50 N with a horizontal force of 35 N at a constant velocity on a horizontal surface. What is the coefficient of kinetic friction?

• 0.7 N

• 15

• 0.7

• 1.4

• 1.4 N

If you are dragging a bag of books horizontally across the floor, and you decrease the number of books in the bag, this will decrease the weight. The friction force between the box and the floor ______.

• decreases
• increases
• is unaffected

Tags

NGSS.HS-PS2-1

Kalina accelerates a 200 N dumbbell upward. He must exert ____.

• 200 N

• more than 200 N

• less than 200 N

Tags

NGSS.HS-PS2-1

Kalina holds a 200 N dumbbell at rest. He must exert ____.

• 200 N

• more than 200 N

• less than 200 N

Tags

NGSS.HS-PS2-1

Match each force with its 3rd law pair.

Groups:

(a) force of earth on chair

,

(b) force of foot on chair

,

(c) force of fist on locker

,

(d) force of earth on me

• force of locker on fist

• force of chair on foot

• force of chair on earth

• force of me on earth

Tags

NGSS.MS-PS2-1

Your cat that weighs 12 N is at rest on the ground. You are pulling up on him with 3.0 N of force. How much is the normal force on the cat?

• 9 N

• 15 N

• 12 N

• 3 N

• 0 N

Tags

NGSS.MS-PS2-2