G A4.3 Friction

Get the Assessment: FA04.3.docx

The Assessment Solved:

Label every force right or left; Label every acceleration as either speeding up (accel) or slowing down (decel)

A 4.25 kg block of wood has a kinetic coefficient of friction of 0.120 and a static of 0.330 between it and the level floor.

0. Calculate the kinetic friction force, and the maximum static friction force. If the block were at rest, and you exerted a force to the right of 15.0 N, would the block begin to move? What if the force was 12.0 N? Support your answer with numbers.

( 5.00 N, 13.7 N, 15.0 N would make it slide because it is bigger than the maximum static friction force of 13.7 N, but 12.0 N would not because it is smaller - you must identify what the forces are, what magnitude (the number) they have, and compare them)

1. If the block is sliding to the right, and I exert a force of 7.80 N to the right, what is the acceleration of the block?

(+0.659 m/s/s, accelerating)

2. If the block is sliding to the left, and I exert a force of 3.50 N to the right, what is the acceleration of the block?

(+2.00 m/s/s, decelerating)

3. If the block is sliding to the right, and accelerating to the right at 2.35 m/s/s, what must be the outside force acting on the block?

(+15.0 N, right)

4. If the block is sliding to the left, but is decelerating at 3.12 m/s/s, what must be the outside force acting on the block?

(+8.26 N, right)

Help with the quizlette:

Basic Friction:

(1-4) A 6.80 kg block of wood has a static coefficient of 0.340 and a kinetic of 0.170 between it and a desk.

1. Calculate the maximum force of static friction

2. Calculate the force of kinetic friction

3. If the block is at rest, and I exert a force of 27.0 N to make it move, does it slide?

Why or why not? Explain your answer with numbers and words.

4. If the block is at rest, and I exert a force of 20.0 N to make it move, does it slide?

Why or why not? Explain your answer with numbers and words. Solution 1 2 3 4

Unknown acceleration: (Use the convention that right is +, left is -, label all accelerations either accel - speeding up, or decel - slowing down)

(5-8) A 5.00 kg box of chocolates has a coefficient of static friction of 0.360, and a kinetic of 0.140 between it and the table. (label all your accelerations accel - speeding up, or decel - slowing down)

5. If the box is sliding to the right and there is a force of 11.0 N to the right, what is the acceleration of the box? Solution 5

6. If the box is sliding to the right, and there is a force of 5.00 N to the right, what is the acceleration of the box? Solution 6

7. If the box is sliding to the left, and there is a force of 23.0 N to the left, what is the acceleration of the box? Solution 7

8. If the box is sliding to the left, and there is a force of 4.00 N to the right, what is the acceleration of the box? Solution 8

Unknown force: (Use the convention that right is +, left is -)

(9-12) A 3.80 kg block of cheese has a coefficient of static friction of 0.830, and a kinetic of 0.250 between it and the table. (label all forces left or right)

9. What outside force would cause it to slide to the right, and accelerate to the right at 5.90 m/s/s? Solution 9

10. What outside force would cause it to slide to the right and decelerate at 1.80 m/s/s? Solution 10

11. What outside force would cause it to slide to the left and accelerate left at 2.70 m/s/s? Solution 11

12. What outside force would make it slide to the left and decelerate at 5.00 m/s/s? Solution 12

More Practice Assessments:

Use the convention that to the right is positive, and to the left is negative. (every answer should be overtly labeled + or -)

Part e from every question is not on the summative assessment, they are there for a challenge (The assessments are like 0. and a. through d.)

1. There is a coefficient of kinetic friction of 0.140 and a static of 0.190 between a 5.20 kg box and the level floor.

0. Calculate the kinetic friction force, and the maximum static friction force. If the block were at rest, and you exerted a force to the right of 15.0 N, would the block begin to move? Support your answer with numbers. 3:25 A4 3 Ex1 #0

a. If the box is sliding to the left, and we exert a force of 5.50 N to the right, what is the acceleration? 3:05 A4 3 Ex1 #a

b. If the box is sliding to the right, and we exert a force of 6.90 N to the left, what is the acceleration? 2:47 A4 3 Ex1 #b

c. The box is sliding to the right, but is decelerating at 3.30 m/s/s, what outside force besides friction is acting on it? 3:31 A4 3 Ex1 #c

d. If the box is sliding and accelerating to the left at 4.90 m/s/s, what force must be acting on it? 2:57 A4 3 Ex1 #d

Problems like e. are not on the assessment - but here it is solved anyway for the gifted:

e. The box slides from rest to the right reaching a velocity of 14.5 m/s in a distance of 16.8 m. What outside force was acting? 3:15 A4 3 Ex1 #e

2. There is a coefficient of kinetic friction of 0.105 and a static of 0.450 between a 4.75 kg block of wood and the level floor.

0. Calculate the kinetic friction force, and the maximum static friction force. If the block were at rest, and you exerted a force to the right of 19.0 N, would the block begin to move? Support your answer with numbers. 2:37 Practice 4 3 #2 0

a. If there is a force of 8.20 N to the right, and the block is sliding to the right, what is the acceleration? 1:45 Practice 4 3 #2a

b. If the block is sliding to the left, and there is a force of 2.70 N to the left, what is the acceleration of the block? 1:20 Practice 4 3 #2b

c. What applied force would make the block accelerate and slide to the right at 4.30 m/s/s? 1:26 Practice 4 3 #2c

d. If the block is sliding to the left, but is decelerating at 7.10 m/s/s, what force must be applied to it? 1:43 Practice 4 3 #2d

e. If you apply 8.90 N to the right and the block starts to slide to the right from rest, what will be the velocity in 8.00 seconds?

3. There is a coefficient of kinetic friction of 0.310 and a static of 0.470 between an 8.35 kg block of wood and the level floor.

0. Calculate the kinetic friction force, and the maximum static friction force. If the block were at rest, and you exerted a force to the right of 45.0 N, would the block begin to move? Support your answer with numbers. 1:50 Practice 4 3 #3 0

a. If the block is sliding to the right, and there is a force of 13.0 N to the right, what is the acceleration? 1:38 Practice 4 3 #3a

b. If the block is sliding to the right, but there is a force of 12.4 N to the left, what is the acceleration? 1:50 Practice 4 3 #3b

c. If the block is sliding to the left, but is decelerating at 2.80 m/s/s, what outside force must be acting? 2:16 Practice 4 3 #3c

d. If the block is sliding to the right, but is decelerating at 7.36 m/s/s, what is the force acting on the block? 2:13 Practice 4 3 #3d

e. From rest the block reaches a speed of 15.0 m/s from rest in a distance of 20.0 m. What force was acting?

4. There is a coefficient of kinetic friction of 0.155 and a static of 0.260 between a 3.10 kg block of wood and the level floor.

0. Calculate the kinetic friction force, and the maximum static friction force. If the block were at rest, and you exerted a force to the right of 6.00 N, would the block begin to move? Support your answer with numbers.

a. If the block is sliding to the right, and you exert a force of 4.19 N to the left, what is the acceleration?

b. If the block is sliding to the left, and you exert a force of 6.32 N to the left, what is the acceleration?

c. If the block is sliding and accelerating to the right at 4.45 m/s/s, what force must be applied?

d. If the block is sliding to the left and accelerating to the left at 1.75 m/s/s, what force must be applied?

e. The block displaces itself to the left 12.0 m from rest in 2.87 s. What force must have acted?

5. There is a coefficient of kinetic friction of 0.235 and a static of 0.385 between an 8.85 kg box and the level floor.

0. Calculate the kinetic friction force, and the maximum static friction force. If the block were at rest, and you exerted a force to the right of 34.0 N, would the block begin to move? Support your answer with numbers.

a. If the box is sliding to the left, and there is a force of 13.5 N to the left, what is the acceleration?

b. If the box is accelerating to the right, and there is a force of 34.7 N to the right, what is the acceleration?

c. If the box is sliding to the right, but is decelerating at 6.50 m/s/s, what force must be acting on the box?

d. If the box is sliding to the left, but is decelerating at 1.29 m/s/s, what must be the force acting on the box?

e. If the box is sliding to the right, and there is a force of 32.0 N to the right, what will be its final velocity from rest when is has gone 45.0 m?

The Instruction for this Unit:

Calculating the force of friction: