Module 10

Question 1

Inertia:

Answer 1

the tendency of an object to resist changes in its velocity.

Question 2

Friction:

Answer 2

A force that opposes motion, resulting from the contact of 2 surfaces.

Question 3

Kinetic Friction:

Answer 3

Friction that opposes motion once the motion has already started.

Question 4

Static Friction:

Answer 4

Friction that opposes the ignition of motion.

Question 5

State Newton’s 3 laws of motion:

Answer 5

1 - an object in motion (or at rest) will tend to stay in motion (or at rest) until acted upon by and outside force.
2- when an object is acted on by one or more outside forces, the total force is equal to the mass of the object times the resulting acceleration.
3- For every action, there is a equal and opposite reaction.

Question 6

In space, there is almost no air, so there is virtually no friction. If an astronaut throws a ball in space with an initial velocity of 3.0 meters per second to the “west,” what will the ball’s velocity be in a year?

Answer 6

Every year it’s velocity will be 3.0 meters per second to the west because their are no other forces acting on it.

Question 7

A boy is running with a beanbag in his hands. He passes a tree, and at the moment he is beside the tree, he drops the beanbag. Will the beanbag land next to the tree? if not, will it be north or south of the tree?

Answer 7

north.

Question 8

Suppose, a Boy is running and his friend is standing next to a tree with a beanbag. As the boy passes, he barely taps the beanbag, causing it to fall out of his friend’s hands, Will the beanbag land next to the tree? If not, will it be north or south of the tree?

Answer 8

It will be beside the tree.

Question 9

A busy shopper is driving down the road. He has many boxes piled in the back seat. Suddenly he must hit the brakes. will the packages slam into the seat behind them or the seat in front of them.

Answer 9

the front seat.

Question 10

When roads get wet, they can get slick. Obviously, then, the friction between a car’s tires and the road decreases when the road is wet. Why?

Answer 10

Because the water fills the groves in the road.

Question 11

In order to slide a refrigerator across the floor, a man must exert an enormous amount of force. Once it is moving, however, the man need not exert nearly as much force to keep it moving. Why?

Answer 11

Because static friction is stronger than kinetic friction.

Question 12

A child is pushing her toy across the room with a constant velocity to the east. If the static friction between this toy and the floor is 15 Newtons, while the kinetic friction is 10 Newtons, what force is the child exerting?

Answer 12

The child is exerting only a little more then the friction and because the toy is moving it is kinetic friction so the answer is
10 Newtons to the east.

Question 13

A father is trying to teach his child to ice skate. As the child stands still, the father pushes him forward with an acceleration of 2.0 meters per second2 north. If the child’s mass is 20 kg, what is the force with which the father is pushing? ( because they are on ice you can ignore the friction)

Answer 13

tF= MA
tF= 200.2=
40 Newtons North.

Question 14

In order to get a 15 kg object moving to the west, a force of more than 25 Newtons must be exerted. Once it is moving, however, a force of only 20 newtons accelerates the object at 0.1 meters per second2 to the west. 1) What is the force that static friction can exert on the object? 2) What is the force of kinetic friction?

Answer 14

the static frictional force is 25 Newtons east.
tF= M*A
tF= (15kg) * (0.1 m/sec2) = 1.5 Newtons
20 Newtons - kinetic frictional force = 1.5 Newtons
18.5 Newtons east.

Question 15

In order to shove a rock out of the way, a gardener gets it moving by exerting just slightly more than 100 Newtons of force. To keep it moving at a constant velocity eastward, however, the gardener needs only to exert a 45-Newton force to the east. What are the static and kinetic frictional forces between the rock and the ground?

Answer 15

Static - 100 Newtons west

Kinetic - 45 Newtons West

Question 16

2 men are trying to push a 710 kg rock. The 1st man exerts a force of 156 Newtons east, and the 2nd man exerts a force of 220 Newtons east. The rock accelerates at 0.2 meters per second2 to the east. What is the kinetic frictional force between the rock and the ground?

Answer 16

tF=M*A
tF=710kg*0.2 Meters/ second2
tF= 142 Newtons 
Fm- Ff= tf 
376- Ff= 142 Newtons 
234 Newtons  west

Question 17

A child pushes against a large doghouse, trying to move it. The dog house remains stubbornly unmoved. What exerts the equal and opposite force which Newton’s 3rd law of motion says must happen in response to the child’s push? What is that force exerted on ?

Answer 17

the equal and opposite force is exerted by the dog house on the child.

Question 18

In a baseball game, a player catches a fast-moving ball. The ball stops in the players hand. 1) what evidence tells you that the player exerted a force on the ball.
2) What exerts the equal and a opposite force required be Newton’s 3rd law? 3) What evidence does the player have for this force?

Answer 18

1) the ball’s velocity changed
2) by the ball on the player
3) The pain of the ball

Question 19

A man leans up against a wall with a force of 20 Newtons to the east. What is the force exerted by the wall on the man?

Answer 19

20 Newtons west.

Question 20

Static friction can exert a force of up to 700 Newtons on a 500-kilogram box of bricks. The kinetic friction force is only 220 Newtons. How many Newtons of force must a worker exert to get the box moving? What force must the worker exert to accelerate the box at 0.1 meters per second2 to the south?

Answer 20

1) It is the opposite of the force so: 700 Newtons South.
2) tf = 500 kg * 0.1 Meters/ Second2
tF = 50 newtons
Fm - Ff = 50 newtons
Fm - 220 = 50 newtons
270 Newtons to the south