Unit 4 Multiple Choice Test

Is it possible for an object moving with a constant speed to accelerate?  Explain. A) No, if the speed is constant then the acceleration is equal to zero. B) No, an object can accelerate only if there is a net force acting on it. C) Yes, although the speed is constant, the direction of the velocity can be changing. D) Yes, if an object is moving it can experience acceleration

Consider a particle moving with constant speed such that its acceleration of constant magnitude is always perpendicular to its velocity. A) It is moving in a straight line. B) It is moving in a circle. C) It is moving in a parabola. D) None of the above is definitely true all of the time.

When an object experiences uniform circular motion, the direction of the acceleration is   A) in the same direction as the velocity vector. B) in the opposite direction of the velocity vector. C) is directed toward the center of the circular path. D) is directed away from the center of the circular path.

Consider a particle moving with constant speed such that its acceleration of constant magnitude is always perpendicular to its velocity. A) It is moving in a straight line. B) It is moving in a circle. C) It is moving in a parabola. D) None of the above is definitely true all of the time.  

What type of acceleration does an object moving with constant speed in a circular path experience? A) free fall B) constant acceleration C) linear acceleration D) centripetal acceleration  

What force is needed to make an object move in a circle? A) kinetic friction B) static friction C) centripetal force D) weight    

When an object experiences uniform circular motion, the direction of the net force is   A) in the same direction as the motion of the object. B) in the opposite direction of the motion of the object. C) is directed toward the center of the circular path. D) is directed away from the center of the circular path.

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 B) 0.5g downward C) g upward D) 2g upward

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 B) (rg)1/2  C) (2rg)1/2  D) (0.5rg)1/2   

A pilot executes a vertical dive then follows a semi-circular arc until it is going straight up.  Just as the plane is at its lowest point, the force on him is A) less than mg, and pointing up. B) less than mg, and pointing down. C) more than mg, and pointing up. D) more than mg, and pointing down.  

A coin of mass m rests on a turntable a distance r from the axis of rotation.  The turntable rotates with a frequency of f.  What is the minimum coefficient of static friction between the turntable and the coin if the coin is not to slip? A) (4π2f2r)/g B) (4π2fr2)/g C) (4πf2r)/g D) (4πfr2)/g

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 B) away from the curve's center C) toward the front of the car D) toward the back of the car  

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) twice as big B) four times as big C) half as big D) one-fourth as big  

A car goes around a curve of radius r at a constant speed v.  Then it goes around a curve of radius 2r at speed 2v.  What is the centripetal force on the car as it goes around the second curve, compared to the first? A) four times as big B) twice as big C) one-half as big D) one-fourth as big

The gravitational force between two objects is proportional to   A) the distance between the two objects. B) the square of the distance between the two objects. C) the product of the two objects. D) the square of the product of the two objects.

The gravitational force between two objects is inversely proportional to   A) the distance between the two objects. B) the square of the distance between the two objects. C) the product of the two objects. D) the square of the product of the two objects.

Two objects attract each other gravitationally.  If the distance between their centers is cut in half, the gravitational force   A) is cut to one fourth. B) is cut in half. C) doubles. D) quadruples

Two objects, with masses m1 and m2, are originally a distance r apart. The gravitational force between them has magnitude F.  The second object has its mass changed to 2m2, and the distance is changed to r/4.  What is the magnitude of the new gravitational force? A) F/32 B) F/16 C) 16F D) 32F

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/16 B) F/4 C) 16F D) 4F

Compared to its mass on the Earth, the mass of an object on the Moon is A) less. B) more. C) the same. D) half as much.

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) 12 kg B) 72 kg C) 72 N D) 12 N

As a rocket moves away from the Earth's surface, the rocket's weight A) increases. B) decreases. C) remains the same. D) depends on how fast it is moving.

A spaceship is traveling to the Moon.  At what point is it beyond the pull of Earth's gravity? A) when it gets above the atmosphere B) when it is half-way there C) when it is closer to the Moon than it is to Earth D) It is never beyond the pull of Earth's gravity.

Suppose a satellite were orbiting the Earth just above the surface.  What is its centripetal acceleration? A) smaller than g B) equal to g C) larger than g D) Impossible to say without knowing the mass. 

A hypothetical planet has a mass of half that of the Earth and a radius of twice that of the Earth.  What is the acceleration due to gravity on the planet in terms of g, the acceleration due to gravity at the Earth? A) g B) g/2 C) g/4 D) g/8

The acceleration of gravity on the Moon is one-sixth what it is on Earth.  The radius of the Moon is one-fourth that of the Earth.  What is the Moon's mass compared to the Earth's? A) 1/6 B) 1/16 C) 1/24 D) 1/96

Two planets have the same surface gravity, but planet B has twice the radius of planet A.  If planet A has mass m, what is the mass of planet B? A) 0.707m B) m C) 1.41m D) 4m

Two planets have the same surface gravity, but planet B has twice the mass of planet A.  If planet A has radius r, what is the radius of planet B? A) 0.707r B) r C) 1.41r D) 4r

Consider a small satellite moving in a circular orbit (radius r) about a spherical planet (mass M).  Which expression gives this satellite's orbital velocity? A) v = GM/r B) (GM/r)1/2  C) GM/r2  D) (GM/r2)1/2 

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 twice the speed of A. B) The speed of B is half the speed of A. C) The speed of B is one-fourth the speed of A. D) The speed of B is equal to the speed of A.

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) greater than their true weight B) equal to their true weight C) less than their true weight D) zero

Who was the first person to realize that the planets move in elliptical paths around the Sun? A) Kepler B) Brahe C) Einstein D) Copernicus

The speed of Halley's Comet, while traveling in its elliptical orbit around the Sun, A) is constant. B) increases as it nears the Sun.   C) decreases as it nears the Sun. D) is zero at two points in the orbit.

The average distance from the Earth to the Sun is defined as one "astronomical unit" (AU).  An asteroid orbits the Sun in one-third of a year.  What is the asteroid's average distance from the Sun? A) 0.19 AU B) 0.48 AU C) 2.1 AU D) 5.2 AU