Question 1

The orbit of Comet UX209 about the Sun is not a circle but it orbits once every 365 days, just as Earth does. UX209 is closer to the Sun in April than it is in October. Thus, the speed of UX209 as it moves along its orbit is

Accepted Answer

Since UX209 orbits once every 365 days, it must have the same period as Earth, which is why it takes the same amount of time to orbit the Sun. Since the orbit of UX209 is not a circle, it means that it must move faster when it is closer to the Sun and slower when it is farther away. Therefore, its speed is greater in April when it is closer to the Sun and slower in October when it is farther away. Choice B is the correct answer.

Question 2

Earth's gravity attracts a person with a force of 120 lbs. The force with which the Earth is attracted towards the person is

Accepted Answer

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Therefore, if the Earth attracts a person with a force of 120 lbs, the person attracts the Earth with an equal force of 120 lbs.

Question 3

For reasons known only to them, a group of extraterrestrials offers you your choice of three gold ingots. One weighs 10 lb on Earth, the second weighs 10 lb on Jupiter, and the third weighs 10 lb on the Moon. To get the most gold, you should choose the ingot that weighs 10 lb on

Accepted Answer

The weight of an object depends on the gravitational force exerted on it. The Moon has a weaker gravitational force compared to Earth and Jupiter. Therefore, an ingot that weighs 10 lb on the Moon would have more mass and thus more gold than one that weighs the same on Earth or Jupiter, where the gravitational forces are stronger.

Question 4

An object undergoes uniform circular motion. Which pair of vectors is perpendicular?

Accepted Answer

In uniform circular motion, the velocity vector and centripetal acceleration vector are perpendicular to each other, as the centripetal acceleration vector always points towards the center of the circle and the velocity vector is tangent to the circle. The centripetal force vector is not necessarily perpendicular to either the velocity or acceleration vectors.

Question 5

After their rocket engines shut off, astronauts experience weightlessness in the orbiting Space Shuttle,

Accepted Answer

When the rocket engines shut off, the astronauts are actually in free-fall towards the Earth, but their forward velocity is what keeps them from falling into the atmosphere. This is why they experience weightlessness. Therefore, choice B is the best answer.

Question 6

A man weighs 650 N while on the surface of Earth. If he is transported to the planet Mythos, which has the same mass as Earth but a radius that is five times larger than Earth's, his weight would be

Accepted Answer

Weight is directly proportional to the mass of the planet and inversely proportional to the square of the radius of the planet. Since Mythos has the same mass as Earth but a radius 5 times larger, the man's weight would be $ \frac{1}{5^2} = \frac{1}{25} $ of his weight on Earth, which is $ \frac{650}{25} = 26 $ N.

Question 7

A rock that weighs 100 lb on Earth is taken to the Moon. Which of the following statements accurately describes what would be observed?

Accepted Answer

The gravitational force on the rock is less on the Moon, which means its weight is less. Mass remains the same regardless of location, so it is not easier or harder to lift based on mass or radius.

Question 8

If a ball at the end of a string is whirled in a vertical circle at constant speed, the tension will be

Accepted Answer

At the highest point in the motion, the tension in the string must be sufficiently large to provide the necessary centripetal force to keep the ball moving in its circular path. At the lowest point in the motion, the tension in the string must be large enough to provide the centripetal force as well as counteract gravity pulling the ball down. Therefore, the tension is greatest at the lowest point in the motion.

Question 9

A car travels around a curve with constant speed. The correct statement from the following is

Accepted Answer

When a car travels around a curve with constant speed, it is still accelerating, even though its speed is constant. This acceleration is directed inward toward the center of the curve, due to the centripetal force needed to maintain the circular motion.

Question 10

The mass of an apple on the Earth is 0.2 kg. On the Moon, the mass of the same apple would be

Accepted Answer

The mass of an object is a property that remains constant regardless of the location. Therefore, the apple would have the same mass of 0.2 kg on the Moon as it does on Earth.

Question 11

A banked curve in a roadway is designed for a speed of 35 mph. During an ice storm cars should be able to safely negotiate this curve at 35 mph, because at this speed

Accepted Answer

The necessary centripetal force to safely negotiate the curve is supplied entirely by the normal force from the road, which is perpendicular to the surface of the road. This normal force increases as the speed of the car increases, allowing the car to safely negotiate the curve at 35 mph.

Question 12

Which of the following is NOT a vector?

Accepted Answer

Mass is a scalar quantity, as it has only magnitude and no direction. The other options (acceleration, weight, and velocity) are all vector quantities.

Question 13

A ball is whirled on the end of a string in a horizontal circle at constant speed. Suddenly, the string breaks. Immediately after the string breaks, the ball will

Accepted Answer

When the string breaks, the only force acting on the ball is its own inertia, which causes it to continue moving in a straight line tangent to the circle. Therefore, the ball will have a horizontal velocity that is tangential to the circle.

Question 14

An asteroid moving around the Sun happens to experience only negligible forces from other objects in the solar system. The path of this asteroid will be

Accepted Answer

According to Kepler's laws of planetary motion, any object moving around the Sun under the influence of negligible forces will follow an elliptical path, with the Sun at one of the foci of the ellipse. Therefore, the correct option is C, an ellipse.

Question 15

A cyclist races around a circular track at the constant speed of 20 m/s. The radius of the track is 40 m. The dentripetal acceleration of the cyclist is

Accepted Answer

The centripetal acceleration of an object moving in a circular path is given by the equation a = v^2/r, where v is the velocity of the object and r is the radius of the circular path. In this case, the cyclist has a constant speed of 20 m/s and is moving in a circular path with a radius of 40 m. Therefore, the centripetal acceleration is a = (20 m/s)^2/40 m = 10 m/s^2, which is directed toward the center of the track. Therefore, the best choice is B.

Question 16

Arnold can bench press 315 pounds in his gym in California. That is exactly six big 45-pound weight plates and the 45-pound bar. He can lift all that one time, but he cannot lift 325 pounds even once. At the NASA gym on the Moon, Arnold would

Accepted Answer

The answer of Arnold can bench press 315 pounds in...

Question 17

An object weighs 30 newtons on Earth. What is its approximate mass?

Accepted Answer

The weight of an object on Earth is given by the formula weight = mass x gravity. With gravity approximately equal to 9.8 m/s^2, a 30-newton object would have a mass of about 3 kg (30 N / 9.8 m/s^2 ≈ 3 kg).

Question 18

Six identical blocks of steel, each with mass 10.0 kg, are taken to the Moon. On the Moon, their combined mass is

Accepted Answer

The mass of an object remains constant regardless of its location. Since each block has a mass of 10.0 kg and there are six blocks, their combined mass is 6 * 10.0 kg = 60.0 kg.

Question 19

Two cars that have the same mass are moving around a circular track at the same constant speed. The track is perfectly level. If car 1 is at the inner edge of the track and car 2 is at the outer edge, then

Accepted Answer

The frictional force, which provides the centripetal force necessary for circular motion, depends on the radius of the circle. Since car 1 is on the inner edge, it travels a smaller circle with a smaller radius, requiring less frictional force than car 2, which travels on a larger circle with a larger radius.

Question 20

Which planets exhibit retrograde motion, that is, periodically appear to reverse their direction of motion across the sky?

Accepted Answer

All of the planets in the Solar System exhibit retrograde motion as observed from Earth. This apparent reversal in their direction of motion across the sky is due to the relative positions and motions of Earth and the other planets in their orbits around the Sun.

Quiz 5: Circular Motion, the Planets, and Gravity