Physics Exam 1 Review (HW 2 &4)

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

-60 N to the right. -30 N to the left. -60 N to the left. D ) none of the above

Which of the following could lead to an objectivity problem?

-A scientist discussing lung diseased who is funded by tobacco companies -A politician from an oil-producing state who is making policy on fuel emissions -A dietitian who happens to sell their own line of all-natural, healthy vitamin supplements. D ) All of the above

Which has zero acceleration?

-an object at rest -an object moving at constant velocity -an object in mechanical equilibrium D ) all of the above

The massive ram of a pile driver falling from rest strikes a pile with a speed that depends on the

-initial potential energy of the ram. -distance the ram falls. -initial height of the ram. D) all of the above

The equilibrium rule F = 0 applies to

-objects or systems in uniform motion in a straight line. -objects or systems at rest. C ) both

The amount of friction that occurs when two blocks slide against each other depends on

-the "stickiness" of atoms on their surfaces. -how much they are pressed together. C ) both

Two identical freight cars roll without friction towards each other on a level track. One car rolls at 2 m/s and the other car rolls at 1 m/s. After the cars collide, they couple and roll together with a speed of

0.5 m/s

A 30-kg girl and a 25-kg boy face each other on friction-free roller blades. The girl pushes the boy, who moves away at a speed of 1.0 m/s. The girl's speed is

0.83 m/s.

When a falling object gains 10 m/s each second, its acceleration is

10 m/s^2

A machine puts out 100 W of power for every 1000 W put into it. The efficiency of the machine is Which of these forms of energy is NOT renewable?

10%

A 1-kg mass at Earth's surface weighs about

10N

Place a book that weighs 10 N on a horizontal surface and the support force on the book is

10N

A ball is moving at 4 m/s and has a momentum of 48 kg·m/s. What is the ball's mass?

12 kg

A car moves 4 times as fast as another identical car. Compared with the slower car, the faster car has

16 times the kinetic energy

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

160N

A car moving at 50 km/h skids 20 m with locked brakes. How far will it skid if its initial speed is 150 km/h?

180 m

Exert 100 J in 50 s and your power output is

2 W

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/s

A 1000-kg car moving at 10 m/s that brakes to a stop in 5 s has an average braking force of

2000N

A 50-N object falling in air experiences 30 N of air resistance. The amount of net force on the falling object is

20N

When the input piston of a hydraulic press is depressed 20 cm, the output piston is observed to move 1 cm. An input force of 1 N can raise no more than

20N

A 2-kg mass that weighs 20 N has 40 J of potential energy relative to the ground. What is its height?

2m

The average speed of a deer traveling a distance of 2 km in a time of one-half hour is

4 km/s

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

4 m/s ^2

A music console is pushed a distance of 2 m with a force of 20 N. The work done on the console is

40 J

A 1-kg ball dropped from a height of 2 m rebounds only 1.5 m after hitting the ground. The amount of energy converted to heat is about

5 J

One-half second after starting from rest, a freely falling object will have a speed of about

5 m/s

A piece of taffy slams into and sticks to another identical piece of taffy that is at rest. The momentum of the two pieces of taffy stuck together after the collision is the same as it was before the collision. Kinetic energy is a different story, for part of it turns into heat. What percentage of the kinetic energy converts into heat?

50%

A diver who weighs 500 N steps off a diving board 10 m above the water hits the water with kinetic energy of

5000 J

A girl pushes a cart to the left with a 100-N force. A boy pushes it to the right with a 50-N force. The net force exerted on the cart is

50N to the left

When a 10-N object is suspended at rest by two vertical strands of rope, the tension in each rope is

5N

A post appears on your social media that describes an article about Genetically-Modified foods. It cites a scientific study sponsored by the World Health Organization, and is published in a peer reviewed journal. It does not draw broad conclusions, but a glance at the source suggests that the data shows the opposite of what the post claimed. This post has a problem with

Accuracy

A site discussing a complicated issue turns up in a web search. Looking it over, you find a number of interesting-looking conclusions based on recent, well cited data about the issue, but the author does not identify themselves or establish why they are qualified to summarize the issue. Their position is contrary to the position of most experts in the field. This article has a problem addressing......

Authority

The ultimate source of energy from fossil fuels is the

Sun

An object weighs 30 N on Earth. A second object weighs 30 N on the Moon. The object with the greater mass is the one on....

The Moon

When you push your desk to the right, friction on the desk acts toward

The left

When you push a crate across a level floor at constant speed, friction between the crate and the floor is

The same amount as your pushing force

The Dunning-Kruger effect is a bias in which people overestimate their understanding of science because

They aren't informed enough

You find an article on the internet that contradicts your existing beliefs. What should you do?

Treat it skeptically

You find an article on the internet that sounds consistent with your existing beliefs. What should you do?

Treat it skeptically

Which of the following has the largest momentum relative to Earth?

a pickup truck speeding along the highway

You're lying on the sand on a breezy day when a pesky fly wishes to join you. The breeze is blowing at a steady 2 m/s. In order for the fly to land on you it should hover over you while flying.....

against the breeze at 2 m/s.

Which has the greatest mass?

automobile battery

While a crate rests on a horizontal floor the friction force acting on the crate is

between 0 and the weight of the crate

Which requires more work: lifting a 50-kg sack vertically 2 m or lifting a 25-kg sack vertically 4 m?

both require the same amount of work

A popular swinging-balls apparatus (Newton's cradle) consists of a series of identical elastic balls suspended by strings so they barely touch each other. When two balls are pulled away from one end and released, they strike the row of balls and two balls pop out from the other end. If instead, one ball popped out with twice the speed, this would be a violation of conservation of

energy

A simple machine CANNOT multiply

energy

A bucket of cement is raised by a rope at constant speed at a construction site. The upward force on the bucket supplied by the rope is

equal to the force of gravity

In contrast to Aristotle's way of explaining nature, Galileo relied on

experiment

The most energy per unit mass can be extracted from

fossil fuel power

You use a straw for a pea shooter. The speed of the pea emerging from the straw when you blow through it will be greater if the straw is

full length

A glance at your speedometer will tell you your

instantaneous speed

Whenever the net force on an object is zero, its acceleration

is zero

When Galileo rolled a ball down an incline and up another incline, he found that the ball rolled nearly to

it's initial height

Compared to a recoiling rifle, the bullet that is fired has a greater

kinetic energy

A ball is projected into the air with 900 J of kinetic energy that is transformed to potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is

less than 900 J

An object may have potential energy because of its

location

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

A heavy truck and a small truck roll down a hill. Neglecting friction, at the bottom of the hill the heavy truck has greater

momentum

An object in motion will continue in motion with

momentum

A dog and a mouse run along a road with the same kinetic energy. The faster runner is the

mouse

If you push for an hour against a stationary wall, you do no work

on the wall

The source of Earth's internal energy involves

radioactivity

Suppose a gun were made of strong lightweight material with a pellet that is more massive than the gun. Then firing speed is greater for the

recoiling gun

It is correct to say that impulse is equal to

the change in momentum

The most underlying feature of machines is

the conservation of energy

No work is done by gravity on a bowling ball that rolls along a bowling alley because

the force on the ball is at right angles to the ball's motion

Your weight is

the gravitational attraction between you and earth

A 50-kg sack is lifted 2 m in the same time as a 25-kg sack is lifted 4 m. The power expended in raising the 50-kg sack compared to the power used to lift the 25-kg sack is

the same

In order 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

The distinction between impulse and force involves the

time the force acts

Strictly speaking, if any electrical device in an automobile is turned on (such as an air conditioner, headlights, or radio), more fuel is consumed by the engine. This statement is

true

If you do work on an object in half the time, your power output is

twice

An object lifted 10 m gains a certain amount of potential energy. If it is lifted 20 m, its gain in potential energy is

twice as much

If you push an object twice as far while applying the same force, you do

twice as much work

When you stand at rest on a floor, the number of vertical forces acting on you is

two

The source of Earth's internal energy involves

uranium

Recoil is noticeable if we throw a heavy ball while standing on a skateboard. If instead we go through the throwing motion but hold onto the ball, without friction effects our net recoil will be

zero

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

Is constant

The conservation of momentum is closely related to

Newton's third law

A kilogram is a measure of an object's

Mass

A magazine article calls to attention a new peer-reviewed scientific study that claims that a global trend on annual precipitation is not seen in a particular region of south-eastern Africa. The author, a professional climatologist, concludes that this new data shows that the trend is false. The problem here is mostly with

Coverage

A newspaper article from 1979 is discussing the general consensus on a scientific topic. It cites numerous peer-reviewed articles and gathers perspectives from experts in the field. A cursory glance at the sources suggests that they have represented everything fairly and correctly. The only issue is with

Currency

The two measurements necessary for calculating average speed are

Distance and Time

A parachutist falling at constant velocity is in a state of

Dynamic Equilibrium