Question 1

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 weight of an object at a height h above the surface of the Earth is given by the formula W = (G*M*m)/(R+h)^2, where G is the gravitational constant, M is the mass of the Earth, m is the mass of the object, R is the radius of the Earth, and h is the height above the surface. Plugging in the given values, we get W = (G*6E24*400)/(4000+4000)^2 = 355.8 lb, which is not equal to 200 lb. Therefore, the statement is false.

Question 2

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 does not change with the change in altitude or distance from the surface of the Earth. This is because mass is an intrinsic property of an object and does not depend on its location. However, the weight of the body changes as it is influenced by the gravitational force of the Earth, which weakens with altitude.

Question 3

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 known as the condition for geostationary orbit, where the centripetal acceleration required to maintain a circular orbit is equal to the acceleration due to gravity on the Earth's surface (g).

Question 4

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 continue moving in a straight line tangent to its circular path, in accordance with Newton's first law of motion, rather than in the direction of the centripetal force.

Question 5

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 9 (not 3) when the distance is tripled. This can be derived from the inverse square law of gravity, which states that the force is inversely proportional to the square of the distance. Thus, if the distance is tripled, the force becomes 1/9 of the original force.

Question 6

Planetary orbits are circles.

Accepted Answer

Planetary orbits are actually elliptical or slightly oval in shape. The circular shape is just an approximation.

Question 7

The displacement vector from the equilibrium position points up.

Accepted Answer

The displacement vector from the equilibrium position can point in any direction, depending on the direction and magnitude of the force that caused the displacement. However, if we're talking specifically about a situation where the object is in simple harmonic motion, then the displacement vector does indeed point up from the equilibrium position when the object is at its maximum displacement.

Question 8

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

This statement is true. Gravitational field lines represent the direction and strength of the gravitational field, and the spacing between the lines indicates the strength of the field. As you move away from a point where the gravitational field is strong, the force of gravity becomes weaker, and the field lines become more spread out.

Question 9

Gravity acts over a limited distance range.

Accepted Answer

Gravity is a force that decreases with distance, but technically it acts over an infinite distance range, albeit with decreasing strength.

Question 10

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

Accepted Answer

Weight is the force exerted by gravity on an object, given as W = mg, where m is the mass and g is the acceleration due to gravity. Therefore, weight and mass are related, but not the same. In this case, the weight of the aircraft is given as 1,500 N, and its mass is calculated as 1,500 N / 9.81 m/s^2 = 153 kg.

Question 11

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

Accepted Answer

The gravitational field near the Earth's surface is directed towards the Earth, not away from it.

Question 12

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 for every action, there is an equal and opposite reaction. So when you push on a wall, you are applying force on it, which in turn applies an equal force back on you, pushing you in the opposite direction.

Question 13

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

Accepted Answer

The gravitational force of the Moon causes a "tidal bulge" on opposite sides of the Earth, which creates a high tide. As the Earth rotates, each point on the planet's surface experiences two high and two low tides each day.

Question 14

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 horizontal speed of a projectile remains constant because there is no force acting on it in the horizontal direction.

Question 15

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 statement is true as field lines represent the direction of the force that would act on a small test charge at that point in the field. The direction of field lines indicates the direction of the electric field vector at that point, which in turn gives the direction of the electric force that would act on a positive test charge placed there. Similarly, the direction of magnetic field lines indicates the direction of the magnetic force that would act on a charged particle moving through the field.

Question 16

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

Accepted Answer

The net force must be constant or increasing for the speed to increase, but it doesn't necessarily have to be increasing.

Question 17

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 force of 5 lbs pushing down on your hand from the bag of sugar is the action, and the force you exert on the bag of sugar to hold it up is the reaction. The two forces are not equal and opposite because they act on different objects.

Question 18

A newton is larger than a pound.

Accepted Answer

A newton is a unit of force in the metric system, while a pound is a unit of force in the imperial system. One pound is approximately equal to 4.448 newtons, making a pound larger than a newton.

Question 19

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

Accepted Answer

When you jump, your legs push against the floor, causing the floor to exert an equal and opposite upward force on you, which propels you into the air. This is due to Newton's third law of motion, which states that for every action, there is an equal and opposite reaction.

Question 20

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 acting on the aircraft is equal to the mass of the aircraft multiplied by the acceleration. In this case, the mass of the aircraft is 1,500 N and the acceleration is 15 m/s². Therefore, the force acting on the aircraft is 1,500 N * 15 m/s² = 2,250 N.

Quiz 2: Newtons Laws