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General Physics > chapter 5: circular motion, gravitation > Flashcards

chapter 5: circular motion, gravitation Flashcards

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1
Q

A space station revolves around the Earth as a satellite, 100 km above Earth’s surface. What is the net force on an astronaut at rest inside the space station?

A

a little less than her weight on Earth

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1
Q

You revolve a ball around you in a horizontal circle at constant speed on a string, P as shown here from above. Which path will
the ball follow if you let go of the string when the ball is at point P?

A

After letting go string, the path the ball will follow is d). Because, at point P Newton’s second law ceases to apply, i.e., the ball is no longer acted upon by a centripetal force. According to Newton’s first law, at that point, the ball tends to continue to move along a straight line.

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2
Q

When an object experiences uniform circular motion, the direction of the acceleration vector is ________

A

directed toward the center of the circle at all times

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3
Q

Astronauts in the International Space Station float because ________

A

they are in a state of constant free fall

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4
Q

If the distance to the Moon were doubled, then the force of gravitational attraction between the Earth and the Moon would be _______ its current strength.

A

a quarter

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5
Q

uniform circular motion

A

An object that travels in a circle at a constant speed

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6
Q

centripetal (“center-seeking”)
acceleration

A

acceleration is directed towards the center of the circle at all
times

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7
Q

A car rounds a curve while maintaining a constant speed. Is there a net force acting on the car as it rounds the curve?

A

Yes, and the car accelerates.

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8
Q

I twirl a bucket of water in a vertical circle. Why doesn’t the
water leave the bucket at the top of the circle?

A

The bucket is accelerating downward faster than the water
can fall out.

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9
Q

I twirl a bucket in a vertical circle of radius 1.6 m. At the top of the circle, find the minimum speed such that the water does not fall out

A
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10
Q

How long should it take a tube with a radius of 𝑅𝑅 = 10 m
to rotate so that a person standing on the inner surface of
the tube experiences normal “Earth gravity” (9.8 ⁄m s2)?

A
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11
Q

You drive your sports car too fast around a curve and
the car starts to skid. What is the correct description
of this situation?

A

The friction between the tires and the road is not strong enough to keep the car moving in a circle.

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12
Q

A 1250-kg car rounds a curve of radius 72 m banked at an angle of 14°. If the car is traveling at 85 km/h, (a) will a friction force be required? (b) If so, how much and in what direction?

A
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13
Q

Newton’s law of universal gravitation?

A

every particle in the
universe attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them

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14
Q

If the distance to the Moon were halved, then the force of attraction between
Earth and the Moon would be

A

four times bigger

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15
Q

At what distance from the Earth will a spacecraft traveling directly from the Earth to the Moon experience zero net force because the Earth and the Moon pull with equal and opposite forces?

A
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16
Q

A mass 𝑚𝑚 is placed halfway between an object of mass 𝑀𝑀 and an object of
mass 3𝑀𝑀. The distance from the mass 𝑚𝑚 to either of the other masses is 𝑑𝑑/2.
What is the magnitude of the total force of gravitation on the mass 𝑚𝑚?

A. ⁄8𝐺𝐺𝑀𝑀𝑚𝑚 𝑑𝑑 2
B. ⁄4𝐺𝐺𝑀𝑀𝑚𝑚 𝑑𝑑 2
C. ⁄3𝐺𝐺𝑀𝑀𝑚𝑚 𝑑𝑑 2
D. ⁄𝐺𝐺𝑀𝑀𝑚𝑚 2𝑑𝑑 2
E. ⁄𝐺𝐺𝑀𝑀𝑚𝑚 4𝑑𝑑 2

A

8𝐺𝐺𝑀𝑀𝑚𝑚 𝑑𝑑 2

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17
Q

If you tripled the mass and doubled the diameter of Earth,
by what factor would 𝑚𝑚 at the surface change?

A
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18
Q

Calculate the period of a satellite orbiting the Moon, 120 km above the Moon’s surface.
Ignore effects of the Earth. The radius of the Moon is 1740 km.

A
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19
Q

You know your mass is 65 kg, but when you stand on a bathroom scale in an elevator the reading indicates that your mass is 76 kg. What is the acceleration of the elevator, and in what direction?

A
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20
Q

How would your weight as measured on a scale at the equator compare to your weight as measured at either the North or South pole? (Assume the Earth is a perfect sphere.)

A

slightly lower

The reading on the
scale will be slightly lower since the net force acting on you must no longer be zero

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21
Q

Assuming the Earth is a perfect sphere, determine how the Earth’s rotation
affects the value of 𝑚𝑚 at the equator compared to its value at the poles.

A
22
Q

Astronauts in the international space station float because:

A

while gravity is trying to pull them down, they are trying to continue on a straight-line path at a high speed, so they continuously “miss” the Earth by overshooting it before falling to the ground.

23
Q

Kepler’s first law

A

the path of each
planet is an ellipse, with the sun at one focus

24
Q

Kepler’s second law

A

each planet moves so that an imaginary line drawn from the
planet to the sun sweeps out equal areas in equal periods of time

-This suggests that planets travel faster when they
are closer to the sun

25
Q

Planet A and planet B are in circular orbits around a distant star. Planet A is 9.0 times farther from the star than is planet B. What is the ratio of their speeds 𝑣𝑣A/𝑣𝑣B?

A
26
Q

Kepler’s third law

A

the ratio of the squares of the periods of any
two planets is equal to the ratio of the cubes of their semi-major axes, 𝑠:

27
Q

If you compare the amount of area per time swept by Earth’s orbit with the amount swept by Jupiter’s, Kepler’s laws would lead you to conclude that:

A

Jupiter sweeps a larger area per time because it has a larger orbital path than Earth

28
Q

This force is responsible for how objects with mass attract each other

A

Gravitational force

29
Q

This force, a combination of the electric and magnetic forces, arises between particles that have positive or negative
charge

A

Electromagnetic force

30
Q

This force holds protons and neutrons together so that they can form an atomic nucleus

A

Strong nuclear force

31
Q

This force is involved in radioactivity

A

Weak nuclear force

32
Q

Is it possible for an object moving with a constant speed to accelerate?

A

Yes, although the speed is constant, the direction of the velocity can be changing.

33
Q

An object moves in a circular path at a constant speed. Compare the direction of the object’s velocity and acceleration vectors.

A

The vectors are perpendicular

34
Q

A particle is moving with constant speed such that its acceleration of constant magnitude is always perpendicular to its velocity. Which of the following statements about the motion of the particle is true?

A

It is moving in a circle

35
Q

A roller coaster car is on a track that forms a circular loop in the vertical plane. If the car is to just maintain contact with track at the top of the loop, what is the minimum value for its centripetal acceleration at this point?

A

g downward

36
Q

A roller coaster car (mass = M) is on a track that forms a circular loop (radius = r) in the vertical plane. If the car is to just maintain contact with the track at the top of the loop, what is the minimum value for its speed at that point?

A

(rg)^1/2

37
Q

A car goes around a curve of radius r at a constant speed v. What is the direction of the net force on the car?

A

toward the curve’s center

38
Q

A car goes around a curve of radius r at a constant speed v. Then it goes around the same curve at half of the original speed. What is the centripetal force on the car as it goes around the curve for the second time, compared to the first time?

A

one-fourth as big

39
Q

The gravitational force between two objects is proportional to _________

A

the product of the two objects’ masses

40
Q

Two objects attract each other gravitationally. If the distance between their centers is cut in half, the gravitational force _________

A

quadruples

41
Q

Two objects with masses m1 and m2 are originally a distance r apart. The magnitude of the gravitational force between them is F. The masses are changed to 2m1 and 2m2, and the distance is changed to 4r. What is the magnitude of the new gravitational force?

A

F/4

42
Q

The acceleration of gravity on the Moon is one-sixth what it is on Earth. An object of mass 72 kg is taken to the Moon. What is its mass there?

A

72 kg

43
Q

Suppose a satellite were orbiting the Earth just above the surface. What is its centripetal acceleration?

A

equal to g

44
Q

Satellite A has twice the mass of satellite B, and rotates in the same orbit. Compare the two satellite’s speeds.

A

The speed of B is equal to the speed of A.

45
Q

A person is standing on a scale in an elevator accelerating downward. Compare the reading on the scale to the person’s true weight.

A

less than their true weight

46
Q

The speed of Halley’s Comet, while traveling in its elliptical orbit around the Sun,

A

increases as it nears the sun

47
Q

What are the four fundamental forces in nature?

A

gravitational, electromagnetic, strong nuclear, weak nuclear

48
Q

What is the centripetal acceleration of a point on the perimeter of a bicycle wheel of diameter 70 cm when the bike is moving 8.0 m/s?

A

1.8 x 10^2 m/s2

49
Q

A car traveling 20 m/s rounds an 80-m radius horizontal curve with the tires on the verge of slipping. How fast can this car round a second curve of radius 320 m? (Assume the same coefficient of friction between the car’s tires and each road surface.)

A

40 m/s

50
Q

A car goes around a flat curve of radius 50 m at a speed of 14 m/s. What must be the minimum coefficient of friction between the tires and the road for the car to make the turn?

A

0.40

51
Q

The gravitational attractive force between two masses is F. If the masses are moved to half of their initial distance, what is the gravitational attractive force?

A

4F

52
Q

A satellite is in a low circular orbit about the Earth (i.e., it just skims the surface of the Earth). How long does it take to make one revolution around the Earth? (The mean radius of the Earth is 6.38 x 106 m.)

A

85 min

General Physics (18 decks)

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