SCEN final exam (chapters 1-11)

The language of science is

mathematics

Scientific equations in a conceptual course are mainly

guides to thinking about the relationships between concepts

In science, an educated guess is a

hypothesis

Success in science is mainly linked to emphasis on

experiments

the two measurements are necessary for calculating

distance and time

a glance at the speedometer on your vehicle will tell your

instantaneous speed

Nellie runs the length of a 100-yard football field in a time of 20 seconds. Her average running speed is

5 yards/seconds

The average speed of Daisy running a distance of 2km in a time of one-half hour is

4 km/h

When Jean hikes a distance of 1 km in a time of one-half hour, her average speed is

2 km/h

The average speed of a horse that gallops a distance of 10 km in a time of 30 minutes is

30 km/h

Distinguish between speed and velocity

speed has a magnitude but no direction is specified; velocity is a vector.

Why do we say that velocity is a vector and speed is not?

velocity includes a direction, and speed does not

Does the speedometer on a vehicle show average speed or instantaneous speed?

instantaneous speed

A mosquito flying at 3 m/s encounters a 3-m/s breeze blowing in the same direction, which gives it a resulting speed over the ground of

6 m/s

A mosquito flying at 3 m/s encounters a 3-m/s breeze blowing in the opposite direction, which gives it a resulting speed over the ground of

0 m/s

You're at rest in a hammock when a hungry mosquito sees you as lunch, while a 2-m/s breeze is blowing. If the mosquito joins you for lunch, it should first hover over you by flying

against the breeze at 2 m/s

While in an airplane flying at 100 km/h you look down from the window and spot another airplane flying at the same speed in the opposite direction. Relative to you, the speed of the spotted plane is

200 km/h

You're driving in a car at 50 km/h and bump into a car ahead traveling at 48 km/h in the same direction. The speed of impact is

2 km/h

When a ball increases in speed by the same amount each second, its acceleration

is constant

If a ball rolls down an inclined plane and gains 4 m/s each second it rolls, its acceleration is

4 m/s²

A motor scooter undergoes acceleration when it

decreases speed, gains speed, changes direction

The acceleration of a cart moving an inclined plane (a ramp)

is constant

an object is pulled with two forced, 10 N northward and 15 N southward. The magnitude of the net force is

5 N

An object is pulled with two forces, 10 N northward and 15 N southward. The direction of the net force is to the

south

An object is pulled with three forces: one at 20 N to the right, another at 40 N to the right, and the third at 30 N to the left. The net force is

50 N to the right

Given that two forces of 10 N and 15 N act horizontally (one dimension) on an object, the net force must

be either 5 N or 25 N

What two properties are necessary for a vector quantity?

magnitude and direction

The support force on a 10-N book that rests on a horizontal surface is

10 N

Joshua stands on a floor that supports him. When Sydney rides piggy-back on Joshua, the support force by the floor beneath Joshua

increases

Daisy weighs 120 N and carries Trixie who weighs 40 N on her back. The support force on Daisy's feet is

160 N

When you stand at rest on a pair of bathroom scales, the readings on the scales will always

add to equal your weight.

When Lillian hangs from a pair of gym rings, the upward support forces by the rings will always

add up to equal her weight.

An 800-N woman stands at rest on two bathroom scales so that one scale shows a reading of 500 N. The reading on the other scale is

300 N

As you jump up and down on a floor, the support force by the floor experiences

changes

When Marie pushes her desk to the right, friction between the floor and the desk acts toward

the left

The resistive force of friction occurs for

solids, liquids, and gases

A crate is at rest on a horizontal floor, with nobody pushing. The friction force acting on the crate is

zero

Marie pushes horizontally on her desk, but not hard enough to get it moving. The friction force acting on the desk is

equal and opposite to her push

If you push to the right on a heavy piece of furniture and it slides, what is the direction of friction on the furniture?

left

Suppose you push to the right on a heavy piece of furniture but not hard enough to make it slide. Does a friction force act on the furniture?

yes, a friction force to the left acts on the furniture

If you push a heavy piece of furniture and it slides at constant velocity, how much friction acts on it compared to your pushing force?

it is a friction force equal to the pushing force and in the opposite

An 800-N man stands at rest with his weight evenly distributed on two bathroom scales. The reading on each scale is

400 N

Shake an object to and fro if you want to judge its

mass

A heavy ball hangs by a string, with a second string attached to its bottom (the figure above). A slow pull on the bottom string breaks the

top string

A heavy ball hangs by a string, with a second string attached to its bottom (the figure above). A quick pull on the bottom string breaks the

bottom string

When the bottom string is pulled slowly in the heavy-ball-and-strings demonstration (the figure above), tension

in the top string is due to your pull plus the weight of the ball

An object that has twice as much mass as another object also has twice as much

inertia

Newton's second law focuses on

acceleration

To steadily (constantly) increase the velocity of something requires a

constant net force

A constant net force on a railroad car produces constant

acceleration

A given net force propels an object along a straight-line path. If the net force were doubled, its acceleration would

double

If an object's mass decreases while a constant force acts on it, the acceleration

increases

A given net force propels an object along a straight-line path. If the mass were doubled, its acceleration would

be half

A 10-kg block is pushed across a friction-free horizontal surface with a horizontal force of 20 N. The acceleration of the block is

2 m/s²

A 10-N block and a 1-N block lie on a horizontal frictionless table. To push them with equal acceleration, we would have to push with

10 times as much force on the heavier block

Which object has zero acceleration?

one in a mechanical equilibrium, one at rest, one moving at constant velocity

Jake pulls on a 25-kg cart with a constant force of 50 N. What is the wagon's acceleration?

2.0 m/s²

A block is dragged at constant velocity across a level surface by a force of 6 N. What is the force of friction between the block and the surface?

6 N

A 1000-kg car accelerates at 2 m/s². What is the net force exerted on the car?

2000 N

As an object freely falls, its

velocity increases

During each second of free fall, the speed of an object

increases by the same amount

The gain in speed each second for a freely falling object is about

10 m/s

Any falling object that gains a velocity of 10 m/s each second has an acceleration of

10 m/s²

At the end of 1/2 second an apple freely falling from rest has a speed of

5 m/s

At the end of 2 seconds of free fall, an apple falling from rest has a speed of

more than 10 m/s

An object in free fall has a speed of 60 m/s. One second later its speed is

70 m/s

A free-falling object has a speed of 30 m/s at one instant. Exactly 2 seconds later its speed will be

50 m/s

The acceleration of a vertically-thrown ball at the top of its path is

10 m/s²

When an apple that weighs 1 N is dropped and freely falls, the net force on the apple is

1 N

A 10-kg brick and a 1-kg book are dropped in a vacuum. The force of gravity on the 10-kg brick is

10 times as much as the force on the 1-kg book

A 10-kg brick and a 1-kg book are dropped in a vacuum. The acceleration of the 10-kg brick is

the same as that of the 1-kg book

A heavy object and a light object in a vacuum are dropped at the same time from rest. The heavier object reaches the ground

at the same time as the lighter object

A heavy rock and a light rock in free fall have the same acceleration. Both rocks have the same acceleration because

ratio of force to mass is the same

If an object's mass is decreasing while a constant force is applied to the object, the acceleration

increases

To say there is no such thing as only one force means

there must also be an oppositely directed force

You cannot exert a force on a wall

unless the wall simultaneously exerts the same amount of force on you

When you rub your hands together, you

cannot push harder on one hand than the other

A player hits a ball with a bat. If one part of the interaction is the bat against the ball, the other part is the

ball against the bat

A martial arts person breaks a board with a blow of 3000 N. The force that acts on the hand is

3000 N

A car traveling at 100 km/h strikes an unfortunate bug that splatters on the windshield. The force of impact is greater on the

same for both

Whenever one object exerts a force on a second object, the second object exerts a force on the first that

is equal in magnitude, occurs simultaneously, is opposite in direction

How many forces are required for a single interaction?

two

For a falling ball the action force is the pull of Earth on the ball. The reaction force is the

pull of the ball on Earth

Earth pulls on the Moon. Similarly the Moon pulls on Earth, evidence that

Earth and Moon pull on each other and earth's and Moon's pulls comprise an action-reaction pair

The force exerted on the tires of a car to directly accelerate the car along a road is exerted by the

road

Arnold Strongman and Suzie Small each pull on opposite ends of a rope in a tug-of-war. The greater force on the rope is exerted by

same by each

Arnold Strongman wearing socks and Suzie Small in gym shoes have a tug-of-war on a polished floor. The likely winner is

Suzie

Both ends of a piece of rope are pulled by two people in a tug-of-war. If each pulls with a 400-N force, the tension in the rope is

400 N

How does a helicopter get its lifting force?

the helicopter exerts a force on the air, pushing air down; the reaction force from the air pushes the helicopter up

It is correct to say that impulse is equal to

the change in momentum

The impulse-momentum relationship is a direct result of

Newton's second law

The distinction between impulse and force involves the

time the force acts

The force of a falling apple hitting the ground depends upon

the speed of the apple just before it hits the ground, whether or not the apple bounces, and the time of contact with the ground

To catch a fast-moving softball with your bare hand, you extend your hand forward just before the catch and then let the ball ride backward with your hand. Doing this reduces the catching force because the

time of catch is increased

A karate expert executes a swift blow and breaks a cement block with her bare hand. The magnitude of the force on her hand is

the same as the force applied to the block

When you jump from an elevated position you usually bend your knees upon reaching the ground. By doing this, the contact time is about 10 times more than for a stiff-legged landing and the average force your body experiences is reduced by

about 10 times

A car traveling along the highway brakes to a stop. A greater braking force is required when the car has

more momentum, more mass, and less stopping distance

Padded dashboards in cars are safer in an accident than non-padded ones because a person hitting the dash has

decreased contact force, and increased time of contact

Compared with falling on a wooden floor, a wine glass may not break when it falls on a carpeted floor because of

longer time to stop

When a boxer is moving away from a punch, the force experienced is reduced because

the time of contact is increased