Unit 3 Test

Question 1

When a small car pulls a trailer for a move, which of the following explains why the trailer moves?

Answer 1

While the force of the trailer on the car is equal and opposite to the force of the car on the trailer, the total of all forces acting on the car are unbalanced.

Question 2

When turning around a circle, a car is subject to a continuous force, but its speed does not necessarily change. Why is this true?

Answer 2

The speed is not changing, but the direction is.

Question 3

Which of the following statements best describes the concept of uniform motion?

Answer 3

In the absence of a net force, a moving body continues moving in a straight line with constant speed.

Question 4

Suppose you are driving a car at a constant speed of 40 mph in a straight line. All of a sudden the road curves to the right but you manage to keep driving at exactly the same speed. Which of the following statements is correct?

Answer 4

There was a net force acting on the car

Question 5

A mass of 4.3 kg is accelerated to 6.0 m / s2 when a force of magnitude F is applied to it. If the same force is applied to a mass of 0.5 kg, what is the acceleration of this mass?

Answer 5

51.6 m / s2

Question 6

Acceleration is _______________ to force and __________________ to mass.

Answer 6

proportional; inversely proportional

Question 7

Two forces are applied on an object with a mass of 5 kg. The object then experiences an acceleration of (-i + 10j) m/s^2. One of the forces is known to be (10i + 20j)N. What is the other force?

Answer 7

(-15i + 30j)N

Question 8

An object with a mass of 5 kg is under a constant force (10i + 20j)N. It is located at the origin of a reference frame and its velocity is (-5i + 30j)m/s. What will be its position 10 seconds later?

Answer 8

(50i + 500j)m

Question 9

A person weighing 600 N (mass = 60 kg) when at rest stands on a scale inside a train. The train begins to accelerate horizontally at a rate of 3.5 m / s2. What reading will the scale then give for the weight of the person? Use 10.0 m / s2 as the acceleration due to gravity on the Earth.

Answer 9

600 N

Question 10

Suppose you carve out a small region exactly at the Earth’s center and stand inside that region. What would you weigh? Assume the Earth is a perfect sphere and has a uniform density.

Answer 10

0

Question 11

In a traffic accident, two motorcycles, A and B, collide with each other. Their total masses are 180 kg and 134 kg. If the more massive one experiences an acceleration of 50 m / s2, what is the acceleration of the other motorcycle?

Answer 11

67 m/s^2

Question 12

Newton’s third law for any two objects, A and B, can be written as which of the following?

Answer 12

FAB = -FBA

Question 13

A spider lowers herself on a single strand of silk at constant speed. Taking into account air resistance, which of the following must be true?

Answer 13

The tension in the silk is less than the spider’s weight

Question 14

A 100 N object sits on a table and is tugged forwards and backwards by forces F1 = 1000 N and F2 = 1500 N, as shown. (Note that the vectors are not drawn to scale.) There are no other forces acting on the object. What is the magnitude of the normal force, FN ?

Answer 14

100 N

Question 15

When designing elevators, it is important to consider the maximum tension a cable will support. Which of the following causes a maximum tension?

Answer 15

accelerating upward

Question 16

As shown, a crate of oranges and a crate of apples, each with a different mass, are attached by a rope (with tension Toa). A second rope (To ) is attached to the crate of oranges, and the entire system is pulled with a constant acceleration a by this rope. Which of the following is true of the tensions?

Answer 16

Toa > To

Question 17

Suppose a parachutist with a mass of 67 kg jumps from an airplane. A few seconds after the person opens the parachute she measures her velocity—she is falling down at constant speed of 15 m / s. What is the force of air drag on her parachute?

Answer 17

656.6 N

Question 18

The diagram shows two carts attached by a string that is threaded through a frictionless pulley. A new force, W, is being applied to the system. Which of the following equations for determining the value of T is correct?

Answer 18

T = M 1a

Question 19

The diagram shows a roller skate on the incline of a hill. The x-coordinate is parallel to the inclined surface. The roller skate has a mass of 5.00*10^-1 kg and is on a hill with a 30 degree incline. The sine of 30 degrees is 0.5. The cosine of 30 degrees is 0.866. The constant g is equal to 9.8 m/s^2. Which of the following are the values of a and N?

Answer 19

a = 4.9 m/s^2
N = 5.00*10^-1 kg * (9.8m/s^2) * 0.866 = 4.2 kg m/s^2

Question 20

In general, the frictional force ____________.

Answer 20

is proportional to the normal force

Question 21

Which of the following statements concerning friction is incorrect?

Answer 21

The force of static friction ( fs ) between parallel surfaces in contact is given by: fs = μN.

Question 22

Consider an object resting on an incline that makes an angle θ with the horizontal. Allow for θ to increase. The angle at which the object will break free and slide is dependent upon which of the following?

Answer 22

the coefficient of static friction

Question 23

Which of the following statements concerning an object in free fall through the atmosphere is incorrect?

Answer 23

The speed of a falling object increases due to the frictional force of air drag.

Question 24

Which of the following is a correct statement concerning the velocity of a particle in uniform circular motion?

Answer 24

The velocity is constantly changing directions.

Question 25

Consider a mass m that is attached to a rope such that the mass is in uniform circular motion. Which of the following is the magnitude of the centripetal force?

Answer 25

mv ^2/r