physical world

The potential energy of a spring of constant k that has been stretched a distance x is given by

(1/2)kx ^2.

The kinetic energy of a body is correctly given by which of the following expressions? (m = mass, v = speed)

(1/2)mv ^2

A ball is allowed to drop from rest. If the upward direction is positive, then after 2 seconds its velocity will be: (tip: velocity is a vector quantity, so your answer has to include the correct direction/sign of velocity vector)

-19.6 m/s.

The mass of an apple on the Earth is 0.2 kg. On the Moon, the mass of the same apple would be

0.2 kg

A student releases a ball from rest on an inclined plane and measures that it travels a distance of 0.8 m in a time of 4.0 s. The average speed of the ball is

0.2 m/s.

Assuming g = 10 m/s 2 and that air resistance is negligible, in 1/2 second a ball dropped from rest will fall (note: downward direction is positive)

1.25 m.

A cyclist races around a circular track at the constant speed of 20 m/s. The radius of the track is 40 m. The centripetal acceleration of the cyclist is

10 m/s^2, toward the center of the track.

In order to find the depth of a well, you drop a stone into it and time its fall. It hits the water after falling for 1.5 s. Assuming that downward direction is positive, the depth of the well is about

11 m.

Suppose one's hand exerts a force of 12 N upward on a book weighing 10 N. The reaction to the force of the hand on the book is a force of

12 N exerted by the book on the hand.

Suppose you climb the stairs of an eight-story building, about 24 m high, and your mass is 70 kg. The gravitational potential energy you gain is about

16,500 Joule.

A car starts from rest and reaches 10 m/s in 5 seconds. The average acceleration of the car is

2.0 m/s^2.

One inch is defined as 2.54 centimeters. The correct expression for a one-inch length, expressed in meters, is

2.54 × 10 ^-2 meters

A box is moved 20 m across a smooth floor by a force making a downward angle with the floor, so that there is effectively a 10 N force acting parallel to the floor in the direction of motion and a 5 N force acting perpendicular to the floor. The work done is

200 J.

A crate is acted upon by a net force of 100 N. An acceleration of 4.0 m/s ^2 results. The weight of the crate is

245 N.

An object weighs 30 newtons on Earth. What is its approximate mass? (Note: g = 9.8 m/s2)

3 kg

A car is decelerating at the rate of 2 km/s^ 2. If its initial speed is 66 km/s, how long will it take the car to come to a complete stop?

33 s.

An iron robot falls from rest at a great height. Neglecting air resistance, what is its speed after it has fallen for 3.5 seconds? (note: use g = 9.8 m/s2)

34.3 m/s

A 10.0 kg block on a smooth horizontal surface is acted upon by two forces: a horizontal force of 70 N acting to the left and a horizontal force of 30 N to the right. The acceleration of the block will be

4.0 m/s ^2 to the left.

A car starts from rest and reaches 20 m/s in 5 seconds. The average acceleration of the car is

4.0 m/s^2.

A 10 kg object dropped from a certain window strikes the ground in 4.0 s. Neglecting air resistance, a 5 kg object dropped from the same window strikes the ground in

4.0 s.

A dog weighs 200 N. What is his approximate weight in pounds (lb)? (1 lb = 4.45 N)

45 lb

For identical cannons and identical projectiles and identical initial speeds, but different pointing angles, the maximum distance for its projectile is attained for the cannon which launches at

45° above horizontal.

In order to go from rest to 50 m/s in 10 s, a jet must be able to accelerate at

5 m/s ^2.

An auto moves 10 meters in the first second of travel, 15 more meters in the next second, and 20 more meters during the third second. The acceleration of the auto is

5 m/s^2.

A block of mass 2.5 kg is acted upon by a single force, producing an acceleration of 2.0 m/s 2. The force has a value of

5.0 N.

A certain parcel of real estate is sold for 5.0 Mega dollars. What is the correct scientific notation for this selling price?

5.0 × 10 ^6 dollars

A body travels at an initial speed of 2.5 m/s. Given a constant acceleration of 0.2 m/s 2, what is the speed of the body at time 25 seconds later?

7.5 m/s.

A scout steps off a distance of 140 steps. If each step is 65 cm, what is the distance in meters?

91 m

The numerical factor 10 ^9 corresponds to what quantity?

A billion

Students often fail to include units with their answers. Science teachers say that units are important. In which one of the following situations would you insist that units be included?

A friend offers you two per mile to help pay for gas on a trip.

1. What is the difference between vector quantity and scalar quantity? Explain and give at least 1 example of each of these quantities.

A scalar quantity is a one dimensional measurement of a quantity, like temperature, or mass. A vector has more than one number associated with it. A simple example is velocity.

The ________ of a pendulum is the amount of time the pendulum takes for one full swing.

period

The study of everyday phenomena allows us to

All of the choices are correct. - develop an appreciation of the physical universe around us. - develop an understanding of the concepts used to describe more abstract concepts. - develop our intuition and adjust our "common sense" to understand these phenomena.

A ball is thrown straight up. It reaches its highest point and then falls back. Which of the following is the correct statement?

At the highest point in its motion, the ball's velocity is zero.

(ball graph) each arrow represents the velocity of the ball. If the billard ball M is traveling straight upward at 2.5 seconds

Billard ball M must be faster then T

In a laboratory on Earth, all the air is pumped from a large tube. A feather and a steel ball are simultaneously released from rest inside the tube. What happens next?

Both objects fall and hit the bottom at the same time.

In his model of the motions of the planets, Copernicus

revived the idea that our solar system is heliocentric (Sun-centered)

A grandfather clock that is regulated by a pendulum is taken to the Moon, where the acceleration of gravity is less. Compared to an identical clock on Earth, the grandfather clock on the Moon will

run slow.

A car driver takes Turn 1 at Daytona International Speedway at a steady 120 mph all the way through the turn. The radius of this turn is 1000 feet. Which statement is true?

Change of direction at constant speed means a change in velocity.

When a scientist wants to strengthen a theory, she can make predictions of measurable events. The theory becomes stronger when

she and other scientists observe and measure the events, and they find that the events agree with the prediction.

A quantity that is a measure of how the distance traveled changes with time is

speed

The motion of a falling object is commonly investigated with the aid of a

stroboscope.

If a curve is banked to accommodate cars traveling at 15 m/s, what will happen during an ice storm (no friction with the road) to a car moving at a faster speed?

It will gradually slide up the bank

The first scientist to determine that the orbits of the planets are ellipses was

Kepler

Which of the following is possessed by a moving object, but not by a stationary object?

Kinetic energy

(graph) Place diagrams in order from the instant it jumps out of. the plane and begins free fall until the time it attains terminal velocity

L, J, Q

The cart on the next page has well-oiled wheels and rolls on a level track. Two external forces are exerted horizontally on the cart. At the point shown the cart is in motion in the direction indicated. Over some time interval, during which the cart's motion is observed, it continues to move in the same direction. The two forces act continuously over this interval. Under these conditions - a) Which strobe pattern below best represents the motion of the cart while it is observed? Explain your reasoning. b) Explain why you rejected each of the other strobe patterns.

Line D best represents the motion of the cart because it shows how it is covering more and more distance with each interval, so it is speeding up and accelerating. The net force would be 3 which would mean it was accelerating. - Line A would not have been the answer because it's a straight line at a constant speed, and it is not it is not accelerated. - Line B would not be the answer because it shows how it is covering less and less distance with each interval, so it is slowing down and decelerating. - Line C would not be the answer because it is also constant just with less dots.

Which of the following is a correct metric unit for volume?

Liters.

Which of the following is NOT a vector?

Mass

Jim exerts a force of 500 N against a 100-kg desk that does not move. Virgil exerts a force of 400 N against a 60-kg desk that moves 2 m in the direction of the push. Mik exerts a force of 200 N against a 50-kg desk that moves 5 m in the direction of the push. The most work is done by

Mik

Kepler's three laws of planetary motion were useful but not considered fully explained until

Newton introduced the law of universal gravitation for astronomical and terrestrial objects.

A ball rolling rapidly along a tabletop rolls off the edge and falls to the floor. At the exact instant that the first ball rolls off the edge, a second ball is dropped from the same height. Which ball, if either, reaches the floor first (neglect air resistance)? Explain using your knowledge about projectile motion.

None - Both balls reach the floor at the same time because they both have the same initial zero y-component of velocity.

A car travels around a curve with constant speed. The correct statement from the following is

the car has an acceleration directed inward toward the center of the curve.

You stand on a scale to measure your weight. The reaction to the force the Earth exerts on you is

the force you exert on the Earth.

When an object is at rest, it might have several forces acting on it. However,

the forces balance out to net force of zero.

1. Is a total mechanical energy conserved in the motion of the pendulum? Will it keep swinging forever? Explain.

Since a pendulum experiences air resistance and friction of moving parts in contact, it will lose mechanical energy and eventually stop swinging.

Physics is considered the "Fundamental Science" because

the ideas and concepts of physics are an important part of the foundation of other sciences.

Which of the following quantities relating to motion is not a vector?

Speed

(graph) The acceleration of the object is equal to zero

The acceleration is never equal to zerp

Which has the greater kinetic energy—a 1-ton car moving at 30 m/s or a half-ton car moving at 60 m/s?

The half-ton car

Two projectiles are launched 50° above horizontal but with different initial speeds. Which of the following must be true while the projectiles are in the air? (Ignore air resistance.)

The horizontal accelerations of both projectiles are the same: zero.

Consider two blocks, one made of wood and the other of lead. They have the same dimensions but the lead is much more massive. If they are dropped and fall long enough to reach terminal velocity, which block experiences a larger force from air resistance?

The lead block

Would the tablecloth trick work if a bath towel were used instead of a tablecloth? Explain.

The tablecloth trick is based on inertia and friction considering a towel would create more friction then a tablecloth it would be harder to do. However, to pull off the tablecloth trick, with a towel heavy dishes work the best because they have more inertia, to stay put. It would have to be pulled very smoothly and rapidly for it to work;

A tortoise and hare cover the same distance in a race. The hare goes very fast for brief intervals, but stops frequently, whereas the tortoise plods along steadily and finishes the race ahead of the hare. - a) Which of the two racers has the greater average speed over the duration of the race? Explain - b) Which of the two racers is likely to reach the greatest instantaneous speed during the race? Explain

The tortoise has the greater average speed since he was the winner. The hare has the greater instantaneous speed since he can go faster.

1. A ball attached to a string is whirled in horizonal circle such that is it moves with constant speed: - a) Does the velocity of the ball change in the process? Explain. - b) Is the acceleration of the ball equal zero? Explain

Yes, the velocity is not constant although the speed is constant. No, the acceleration is not zero, as a non-zero acceleration is needed to change velocity

1. A sled is given a push at the top of a hill. Is it possible for the sled to cross a hump in the hill that is higher than its starting point under these circumstances? Explain.

Yes. This is because it will build up enough potential / kinetic energy to get over the hump. Especially if you can assume it is frictionless.

Assume that you're not wearing your seat belt and the car stops suddenly. Why would your head hit the windshield? Explain, using one or more of Newton's laws of motion.

Your head would hit the windshield because your body/head was in motion. When the car stopped your body wants to stay in motion. That is why your head would hit the windshield which is based on newtons first law.

1. An ice skater glides across a frozen pond at a constant velocity. What is the net force acting on the skater? Explain based on Newton's Laws.

Zero, because objects in motion remain in motion in a straight line unless acted upon by an unbalanced force.

A certain force causes a 50 kg person to accelerate at 1.0 m/s ^2. The same force applied to a 75-kg person would cause

a smaller acceleration.

A body whose velocity increases by a constant amount each second is exhibiting motion for which the ________ is constant.

acceleration change in velocity

A quantity that is a measure of how the velocity of a body changes with time is

acceleration.

(graph) An objects distance traveled as a function of time is shown in the graph above. the graph shows

an object moving forward

An object is acted upon by the three forces shown above. In order to move the object upward,

any upward force can be applied.

A car traveling at constant speed

can change direction.

Which of the following units is not appropriate for measuring volume?

centimeter.

If work was done on an object, the object must have

changed its position.

The principal advantage of metric units over English units is that

conversions between units are easier.

An object moving at 30 m/s has an acceleration of -2.0 m/s/hr. Its speed

decreases very slowly.

A student plots data for the velocity of a body versus the time on a graph. The area under the curve on the graph may be identified as:

distance

A box is pushed across a rough horizontal floor by a force acting parallel to the floor in the direction of motion. A force doing negative work on the body is

friction.

Car A travels with speed v around curve number one, which has a radius r. Car B travels with speed 2v around curve number two, which has a radius 2r. The acceleration will be

greater for car B.

If a ball at the end of a string is whirled in a vertical circle at constant speed, the tension will be

greatest at the lowest point in the motion

A ball is whirled on the end of a string in a horizontal circle at constant speed. Suddenly, the string breaks. Immediately after the string breaks, the ball will

have a horizontal velocity that is tangential to the circle

(graph) the magnitude of the acceleration of the object is the largest

in region B

(graph) the speed of the object is largest

in region D

The velocity of a body is graphed as a function of time. The slope of the graph at any point may be identified with

instantaneous acceleration.

Suppose a graph of position versus time is constructed. The slope of the graph at any point may be identified with

instantaneous velocity.

You spin your little brother on a "helicopter" ride, which means you hold hands and spin around a vertical axis, usually resulting in the little brother's feet lifting off the ground. During the "ride", the acceleration of your brother is

inward toward you, and you must pull him inward.

You travel 2640 feet in thirty seconds while in a 65 mi/hr zone. (There are 5280 ft in one mi.) Your average speed is

less than the speed limit.

A refrigerator weighing 1500 N is to be lifted onto a truck bed that is 1.0 m above the ground. When pushed up a slanting ramp 2.0 m in length a force of only 700 N is required to move it at constant velocity. Comparing the work involved in lifting the refrigerator straight up to the work in pushing it along the ramp, there is

less work required when the ramp is employed.

Which of the following is NOT an appropriate unit for measuring acceleration?

m/s

The amount of inertia a body has can be measured by finding its ________.

mass

The development of physics concepts depends heavily on measurements because

measurements are needed to prove ideas true or false.

The conversion of the initial potential energy of a person on a sled on a smooth icy slope into kinetic energy at the bottom is an example of the principle of conservation of ________.

mechanical energy

Two pieces of kryptonite, #1 and #2, have identical masses, but the net force applied to #1 is 400 N and to #2 is 20 N. The acceleration

of #1 is larger.

According to Newton's Law of Gravitation, if the distance between two bodies is doubled the attractive force between them becomes

one quarter as large

A mass hangs on a spring held in a physicist's hand. When the mass is pulled down and then released, it oscillates with a period of 2.0 s. This system is taken to the Moon, where the acceleration of gravity is less. The spring on the Moon is held in an astronaut's hand, and the mass, when pulled down and released, will

oscillate with an unchanged period.

The acceleration of gravity on the Moon's surface is about 1/6 of that on the Earth's surface. An object on the Earth is to be taken to the Moon. We can state that, compared to the Earth,

the object's mass will be the same but the weight will be less on the Moon.

A ball at the end of a string is swinging as a simple pendulum. Assuming no loss in energy due to friction, we can say for the ball that

the potential energy is maximum at each end of the motion.

If the kinetic energy of an object increases, then

the speed must increase as well.

Suppose a theory is used to make a prediction. A measurement is carried out to test the prediction. The measurement is found to have a value far larger than the prediction. This means

the theory might have correct elements but must be modified to account for some unforeseen influences.

An elevator is being lifted upward at a constant speed by a steel cable. All frictional forces are neglected. In this situation, forces on the elevator are such that

the upward force by the cable is equal to the downward force of gravity.

The directions of the velocity and acceleration of an object which is thrown straight upward and then falls back down (ignore the effects of air resistance) have the following characteristics:

the velocity changes direction but the acceleration always stays the same

A physics professor places a soda pop can on the table and asks a student to identify the forces acting upon the can and the directions of each force. The two forces acting on the soda pop can are

the weight force downward and normal force from the table upward.

A body moving in a circular path at constant speed exhibits acceleration because its ________ is changing.

velocity direction

You toss a ball straight up in the air. At the highest point, the ball's

velocity is zero and the acceleration is downward.

The acceleration of a body is given by the slope of a graph plotting

velocity versus time.