physics exam 3.7

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) 4pi^2 f^2 r)/g

9) 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) g downward

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) toward the curve's center

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

B) (rg)1/2

2) 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.

B) It is moving in a circle.

5) 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.

B) It is moving in a circle.

3) An object moves in a circular path at a constant speed. Compare the direction of the object's velocity and acceleration vectors. A) Both vectors point in the same direction. B) The vectors point in opposite directions. C) The vectors are perpendicular. D) The question is meaningless, since the acceleration is zero.

C) The vectors are perpendicular.

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

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

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

C) centripetal force

4) 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.

C) is directed toward the center of the circular path.

8) 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.

C) is directed toward the center of the circular path.

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

C) more than mg and pointing up

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

D

6) 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

D) centripetal acceleration