Deck 3: Forces

Question 1

The SI unit of force is the newton. Express the newton in terms of basic SI dimensions, mass M, length L, and time T.

A)L M^-1 T^-2
B)L^-1 M^-1 T²
C)L M T^-2
D)L M^-1 T²

Answer 1

L M T^-2

Question 2

Some bodies in our solar system are listed in Table 3.1, with masses and radii.

Based on the data in Table 3.1, what is the relationship between the weights of the same object on Earth and the Moon?

A)The weight of the object on Earth is 6 times the weight of the object on the Moon.
B)The weight of the object on Earth is 6 times smaller than the weight of the object on the Moon.
C)The weight is the same on Earth and the Moon.
D)The weight of the object on Earth is 22 times the weight of the object on the Moon.

Answer 2

The weight of the object on Earth is 6 times the weight of the object on the Moon.

Question 3

The coefficient of static friction between a set of tires on a car and a steep road is 0.58. What is the steepest angle of the road on which the car can stay at rest without slipping downhill?

A)15°
B)30°
C)45°
D)60°

Answer 3

30°

Question 4

You drop two iron marbles into a jar of honey. The area of the larger marble is 9 times the area of the smaller one. If the velocity of the smaller marble is half the velocity of the large one, what is the ratio of the viscous forces on the two marbles?

A)The viscous force on the large marble is 6 times greater than on the small marble.
B)The viscous force on the small marble is 6 times greater than on the large marble.
C)The viscous force on the large marble is 18 times greater than on the small marble.
D)The viscous force on the small marble is 18 times greater than on the large marble.

Question 5

A 6 kg box on a 30° incline is held parallel to the incline by a spring attached to the wall. The box is NOT moving. What is the extension of the spring if the spring constant is 100 N/m?

A)0.03 m
B)0.06 m
C)30 cm
D)60 cm

Question 6

Gravity on the Moon's surface is less than gravity on Earth's surface. For two identical objects, one on Earth and the other on the Moon, how do the mass and weight compare?

A)The mass and the weight of the object on the Moon are larger than the mass and the weight of the object on Earth.
B)The masses of both objects are the same, but the weight of an object on the Moon is less.
C)The weights of both objects are the same, but the mass of an object on the Moon is less.
D)The objects in both places have the same mass and the same weight.

Question 7

If you pull a sled up a slope, which one of these statements is correct for the magnitude of a normal force?

A)It is less than the weight of the sled.
B)It is larger than the weight of the sled.
C)It is equal to the weight of the sled.
D)It is zero.

Question 8

For two bodies gravitationally interacting with each other, if you double each mass and halve the distance between them, by how much would the gravitational force change?

A)increase 8 times
B)increase 16 times
C)decrease 8 times
D)decrease 16 times

Question 9

Two identical boxes are on an inclined plane. Box 1 slides down, while box 2 remains at rest on the incline. What of these statements can we correctly conclude?

A)The frictional force is the same for boxes 1 and 2.
B)The frictional force on box 1 is larger than on box 2.
C)The frictional force on box 2 is larger than on box 1.
D)We need to know the weights of the two boxes to draw a conclusion about frictional forces.

Question 10

Which of these forces is the weakest of all fundamental forces?

A)the gravitational force
B)the weak nuclear force
C)the strong nuclear force
D)the electromagnetic force

Question 11

Two identical spheres are resting on a horizontal surface at a distance of 0.01 m from each other, each attached to an identical unstretched spring with a spring constant of 100 N/m. If we charge the spheres with a negative charge of -1.60 µC each, what is the compression of each spring? Coulomb's constant is k = 9.0 × 10⁹ N m²/C².

A)0.14 m
B)0.18 m
C)0.32 m
D)0.36 m

Question 12

Which of the following statements is correct for the force of static friction between two surfaces?

A)It depends on the contact area.
B)It is proportional to the normal force.
C)It is larger than the applied force.
D)It is smaller than the applied force.

Question 13

A 50 kg skier is pulled up a 28° slope at a constant speed by a friend applying a force of 300 N. What is the coefficient of kinetic friction between the snow and the skier?

A)0.18
B)0.30
C)0.36
D)0.63

Question 14

Which of the following is NOT a fundamental force?

A)frictional force
B)electromagnetic force
C)weak nuclear force
D)gravitational force

Question 15

You push a chair across the floor and it moves with a constant velocity. Which of the following statements is true for the force of friction?

A)The force of friction is less than the force with which the chair is being pushed.
B)The force of friction is equal to the force with which the chair is being pushed.
C)There is not enough information for a conclusion.
D)The force of friction is zero.

Question 16

A bird rests at the centre of a thin rope suspended between two poles 0.5 m apart. The rope sags 2 cm under the bird's weight, and the tension in each side is 5 N. What is the mass of this bird?

A)200 g
B)100 g
C)50 g
D)25 g

Question 17

Some bodies in our solar system are listed in Table 3.1, with masses and radii.

Based on the data in Table 3.1, what is the mass of an object on Jupiter, when its measured weight on Earth is 21 N?

A)2.1 kg
B)5.3 kg
C)2.1 N
D)53 N

Question 18

Two identical spheres are resting on a horizontal surface at a distance of 0.04 m from each other, each attached to an identical unstretched spring with a spring constant of 100 N/m. If we charge the spheres with a negative charge of -1.60 ìC each, what is the new spacing between the spheres? Coulomb's constant is k = 9.0 × 10⁹ N m²/C².

A)0.14 m
B)0.18 m
C)0.32 m
D)0.36 m

Question 19

A child manages to use his feet to stop and rest on a slide before he starts gliding again. Choose the free body diagram from below that correctly describes the forces acting on the child while he is at rest.

A)
B)
C)
D)

Question 20

A ball is thrown up in the air. Halfway to its maximal height, what is the net force acting on the ball? Assume that there is no air resistance.

A)The net force is 0 N.
B)The net force is less than its weight.
C)The net force is greater than its weight.
D)The net force is equal to its weight.

Question 21

For the law of gravity equation, F = Gm₁m₂/r², to be dimensionally consistent, what must be the units of universal gravitational constant?

Question 22

Using data from Table 3.3, calculate the ratio between the electrostatic force and the gravitational force between the proton and the electron in a hydrogen atom, if the distance between the electron and the proton is r = 5.3 × 10⁹ m. The universal gravitational constant G = 6.67 × 10^-11 m³ kg^-1 s^-2, and Coulomb's constant k = 9.0 × 10⁹ N m²/C².

Question 23

Which one is stronger, the gravitational force with which you attract Earth or the gravitational force that Earth exerts on you?

Question 24

The gravitational force with which Earth attracts you is larger than the force with which you attract Earth.

Question 25

If you are trying to push a crate along a rough floor and it does not move, there is static friction acting between the floor and the crate. The magnitude of static friction is always larger than the applied force; therefore, the object does not move.

Question 26

We are trying to move a crate across a rough surface. We keep increasing the force until the crate starts moving. Since there is a range of magnitudes of a force, this means that kinetic friction has a range of values before the crate starts moving.

Question 27

The origin of contact forces is electromagnetism.

Question 28

We are trying to move a crate across a rough surface. We keep increasing the force until the crate starts moving. Since there is a range of magnitudes of force applied before the crate starts moving, does this mean that kinetic friction has a range of values as well?

Question 29

Normal force is always a response of a surface to the entire weight of the body.

Question 30

Since viscous forces in fluid and air drag are the same in nature, both depend linearly on the object's velocity.

Question 31

From the data for Earth and the Moon in Table 3.2, how many times stronger is Earth's gravitational field than the Moon's?

Question 32

What is the difference between mass and weight?

Question 33

If a 50 kg skier is pulled by a rope up a 15° slope, what is the minimum tension in the rope? The coefficient of friction is 0.2.

Question 34

Although gravity accelerates you when you fall freely, it is possible to achieve a constant velocity after you jump from an airplane.

Question 35

If the weight of a chest is 560 N, and you try to push it along the floor with a force of 295 N, and the coefficient of static friction between the floor and the chest is µ = 0.5, will the chest move?

Question 36

When a muscle contracts it can pull, and when it stretches it can push.

Question 37

You are standing on the floor, not moving. This means that there is no gravity acting on you.

Question 38

Viscous force in a fluid is what is called drag in the air.

Question 39

The surface tension of water makes it possible for certain insects to walk on the surface of water. What is the origin of surface tension?

Question 40

Can gravity act as a restoring force? Give an example.