Physics exam

For an angle 𝜃 measured from the positive x-axis, the values of sin(𝜃) and cos(𝜃) are always which of the following?

greater than or equal to −1 and less than or equal to 1

A ball is thrown straight up in the air. For which situations are both the instantaneous velocity and the acceleration zero? (Select all that apply.)

None

If the velocity of a particle is nonzero, can the particle's acceleration be zero?

Yes. If the velocity is nonzero, the particle is in motion. If the acceleration is zero, it is constant.

Suppose you are carrying a ball and running at a constant speed, and wish to throw the ball and catch it as it comes back down. Neglecting air resistance, you should do which of the following?

throw the ball straight up in the air and maintain the same speed

What is its acceleration in the vertical direction? (Let up be the positive direction.)

-9.8

Determine which of the following moving objects obey the equations of projectile motion developed in this chapter. (Select all that apply.)

-a ball is thrown in an arbitrary direction. -a rocket moves through the sky after its engines have failed.

An object with a mass of 1 kg weighs approximately 2 lb. Use this information to estimate the mass of the following objects. A baseball

.10 kg

Estimate the order of magnitude of the length, in meters, of each of the following. A mouse

.10 m

What is its acceleration in the horizontal direction?

0

a pool cue

1 m

Your physics textbook

10 kg

A pickup truck

1000

a city block

1000m

an elephant

100m

Estimate the number of atoms in 1 cm3 of a solid. (Note that the diameter of an atom is about 10−10 m.)

10^24

Estimate the number of times your heart beats in a month

10^6

Estimate the number of human heart beats in an average lifetime.

10^9

Find the order of magnitude of your age in seconds

10^9 s

Suppose two quantities, A and B, have different dimensions. Determine which of the following arithmetic operations could be physically meaningful. (Select all that apply.)

AB A/B

Which are equal to zero throughout the motion? Ignore any effects of air resistance. (Select all that apply.)

Ax

Consider the following controls in an automobile: gas pedal, brake, steering wheel. Which controls in this list cause an acceleration of the car? (Select all that apply.)

Brake, steering wheel, gas pedal

A baseball is thrown from the outfield toward the catcher. When the ball reaches its highest point, which statement is true?

Its velocity is perpendicular to its acceleration.

Suppose the displacement x of another object is related to time t according to x = A sin(2𝜋ft), where A and f are constants. What are the dimensions of A? (Hint: A trigonometric function appearing in an equation must be dimensionless.)

L

Suppose that the displacement x of an object is related to time t according to the expression x = Bt2. What are the dimensions of B?

L/T^2

Must two quantities have the same dimensions if you are dividing them?

No

Must two quantities have the same dimensions if you are multiplying them?

No

Two projectiles are thrown with the same initial speed, one at an angle 𝜃 with respect to the level ground and the other at angle 90° − 𝜃. Both projectiles strike the ground at the same distance from the projection point. Are both projectiles in the air for the same length of time?

No

The left side of an equation has dimensions of length and the right side has dimensions of length squared. Can the equation be correct?

No, because the equation is dimensionally inconsistent.

Two cars are moving in the same direction in parallel lanes along a highway. At some instant, car A is traveling faster than car B. Does that mean the acceleration of A is greater than that of B at that instant?

No. Acceleration only tells how an object's velocity is changing at some instant.

As a projectile moves in its path, is there any point along the path where the velocity and acceleration vectors are parallel to each other? (Assume the object is thrown upward and forward, but not straight up.)

No; In order for the velocity and acceleration to be parallel, the x component of the velocity would have to drop to zero. However, velocity of x always remains equal to its initial value; therefore, the velocity and the acceleration can never be parallel.

Lacking modern timepieces, early experimenters sometimes measured time intervals with their pulse. Why was this a poor method of measuring time?

Pulse rates vary for many reasons and differ from person to person.

A boat is heading due south at speed v when passengers onboard spot a dolphin swimming due west away from them, relative to their moving boat. Which of the following must be true of the dolphin's motion relative to a stationary observer floating in the water?

The dolphin is heading west of south at a speed greater than v

An object moves along the x-axis, its position given by y(t) = −3 + 4t. Which of the following cannot be directly obtained from a graph of y vs. t?

The acceleration at any instant

A student throws a heavy red ball horizontally from a balcony of a tall building with an initial speed v0. At the same time, a second student drops a lighter blue ball from the same balcony. Neglecting air resistance, which statement is true?

The balls reach the ground at the same instant.

List some advantages of the metric system of units over most other systems of units. (Select all that apply.)

The metric system uses a single base unit of measure for each physical quantity. Metric measurements are set by international agreement and are the same in every country.

A projectile is launched at some angle to the horizontal with some initial speed vi, and air resistance is negligible. Is the projectile a freely falling body?

Yes

As a projectile moves in its path, is there any point along the path where the velocity and acceleration vectors are perpendicular to each other? (Assume the object is thrown upward and forward, but not straight up.)

Yes

Can it ever be less

Yes

Can the instantaneous velocity of an object at an instant of time ever be greater in magnitude than the average velocity over a time interval containing that instant?

Yes

If a car is traveling eastward, can its acceleration be westward?

Yes

If the velocity of a particle is zero, can the particle's acceleration be nonzero?

Yes

Must two quantities have the same dimensions if you are adding them?

Yes

Must two quantities have the same dimensions if you are equating them?

Yes

Must two quantities have the same dimensions if you are subtracting them?

Yes

Two different measuring devices are used by students to measure the length of a metal rod. Students using the first device report its length as 0.5 m, while those using the second report 0.502 m. Can both answers be correct?

Yes, because their values are the same when both are rounded to the same number of significant figures

a basketball court

between 100 m and 1000 m

A tennis player on serve tosses a ball straight up. As the tennis ball travels through the air, its speed does which of the following?

decreases then increases

Newton's law of universal gravitation can be expressed by the equation F = G Mm r2 , where F is the gravitational force, M and m are masses, and r is a length. Force has the SI units kg · m/s2. What are the SI units of the proportionality constant G?

m3/ kg x s^2

As a projectile moves in its parabolic path, the velocity and acceleration vectors are perpendicular to each other at which of the following along the projectile's path?

peak

A tennis player on serve tosses a ball straight up. While the ball is in free fall, its acceleration does which of the following?

remains constant