Question 1

Just above the surface of the Earth, the direction of the gravitational field is away from the Earth.

Accepted Answer

The direction of the gravitational field is towards the Earth, not away from it.

Question 2

Planetary orbits are circles.

Accepted Answer

Planetary orbits are actually ellipses, meaning they are elongated circles.

Question 3

A body on the surface of the Earth weighs 400 lb. The radius of the Earth is about 4,000 miles. If this same body were placed on a 4,000-mile high tower, its weight would be 200 lb.

Accepted Answer

The gravitational force acting on an object is proportional to the mass of the object and the mass of the planet it is on, and inversely proportional to the square of the distance between the centers of the two objects. Therefore, as the distance between the body and the center of the Earth increases, the gravitational force decreases. However, a 4,000-mile high tower would place the body beyond the atmosphere and into outer space, where the force of gravity would be negligible. Therefore, the weight of the body would not be 200 lb, but rather effectively zero.

Question 4

An aircraft weighing 1,500 N has a mass of 153 kg.

Accepted Answer

True. The weight of an object is equal to its mass multiplied by the acceleration due to gravity (W=mg). Therefore, 1500N = 153kg x 9.81 m/s^2.

Question 5

As you go from a point where a gravitational field is strong to a point where the gravitational field gets weaker, the gravitational field lines get farther apart.

Accepted Answer

Gravitational field lines represent the strength and direction of the gravitational field. When the field is stronger, the lines are closer together, and when the field is weaker, the lines are farther apart.

Question 6

A ball on a string is being whirled around overhead when the string breaks.  The ball will move in the direction of the centripetal force the moment the string breaks.

Accepted Answer

The ball will not move in the direction of the centripetal force. Instead, it will fly off in a straight line tangent to the circle it was previously following.

Question 7

An aircraft weighing 1,500 N is accelerated at 15 m/s², the force acting on the aircraft is 2,295.9 N.

Accepted Answer

The force required to accelerate an object is given by the equation F = ma, where F is the force, m is the mass, and a is the acceleration. 
In this case, the mass of the aircraft is given as 1,500 N. 
The acceleration is given as 15 m/s^2. 
So, the force required to accelerate the aircraft is:
F = ma = 1,500 N x 15 m/s^2 = 22,500 N
Therefore, the force acting on the aircraft is greater than 2,295.9 N. Thus, option B is incorrect. Therefore, the correct answer is A.

Question 8

As you go higher and higher above the surface of the Earth, the mass of a body stays constant.

Accepted Answer

The mass of a body is an inherent property and does not change with distance from the Earth's surface. However, its weight can vary with distance due to the changes in gravitational force.

Question 9

A satellite orbiting the Earth in a circular orbit at 400 miles from the center of Earth is moved to a distance of 1,200 miles from the center of Earth.  The gravitational force between the Earth and satellite changes by a factor of 3.

Accepted Answer

The gravitational force between the Earth and satellite changes by a factor of (r1/r2)^2, where r1 and r2 are the initial and final distances between the Earth and satellite, respectively. Thus, (r1/r2)^2 = (400/1200)^2 = 1/9. This means that the gravitational force decreases by a factor of 9, not 3 as stated in the question. Therefore, the statement is false.

Question 10

To hold a 5 lb bag of sugar in your hand, you must push upwards on it with a force of 5 lb. This is an example of Newton's third law.

Accepted Answer

Newton's third law states that for every action, there is an equal and opposite reaction. In this case, the sugar exerts a downward force of 5 lb on your hand, which is equal and opposite to the force that you exert on the sugar.

Question 11

Tides are caused because different parts of the Earth's oceans are at different distances from the Moon.

Accepted Answer

The gravitational pull of the Moon causes the water in the oceans to bulge, creating high tides, while the areas between the bulges experience low tides.

Question 12

When you jump, you accelerate upward because the floor exerts an upward force on you.

Accepted Answer

According to Newton's Third Law, every action has an equal and opposite reaction. Therefore, when you push down on the floor to jump, the floor exerts an equal and opposite force upward on you, resulting in your acceleration upwards.

Question 13

Gravity acts over a limited distance range.

Accepted Answer

Gravity is a force that acts over an infinite distance range, meaning its effect can be felt between any two objects regardless of their separation distance. However, the strength of the gravitational force diminishes with increasing distance between the objects.

Question 14

If a body were in orbit very near the surface of the Earth, its centripetal acceleration would be equal to g .

Accepted Answer

This is true because the centripetal acceleration required to maintain an object in a circular orbit around the Earth is equal to the acceleration due to gravity, which is represented by g.

Question 15

A newton is larger than a pound.

Accepted Answer

A newton is a unit of force in the International System of Units (SI), and a pound is a unit of mass in the Imperial system. However, when comparing force, 1 pound-force equals approximately 4.44822 newtons, making a newton smaller than a pound-force.

Question 16

You push on a wall, and the wall pushes back on you with the same force. This is an example of Newton's third law.

Accepted Answer

Newton's third law states that every action has an equal and opposite reaction. In this case, the action is the force you apply on the wall, and the reaction is the force the wall applies back on you with the same magnitude.

Question 17

A body is oscillating up and down at the end of a spring. Let's consider when the body is at the top of its up-and-down motion. 
The displacement vector from the equilibrium position points up.

Accepted Answer

When the body is at the top of its up-and-down motion, it has maximum displacement from the equilibrium position, which is downward. However, the displacement vector from the equilibrium position is always opposite in direction to the force acting on the body, which points upward (in this case, the force is the tension in the spring).

Question 18

As an artillery shell travels from the gun to the target, the projectile's vertical speed changes, but its horizontal speed stays constant.

Accepted Answer

The answer of As an artillery shell travels from the...

Question 19

The direction of a field line at a point in space shows the direction of the force that would act on a body placed at the point.

Accepted Answer

This is one of the fundamental principles of field lines in physics. The direction of a field line represents the direction of the force that would act on a hypothetical test object placed at that point in the field.

Question 20

When a body moves in a straight line with increasing speed, the net force on it must be increasing.

Accepted Answer

When a body moves in a straight line with increasing speed, it means there is a net force acting on it, but this does not necessarily mean the net force is increasing. The net force could be constant, and the object would still accelerate.

Quiz 2: Newton S Laws