Question 1

Which of the following best describes the direction of the instantaneous velocity of an object in uniform circular motion?

Accepted Answer

It is always tangent to the circle.

Question 2

A ball of mass $$m is $$attached to a string and revolves in a horizontal circle of radius $$r at $$constant speed $$v. $$What is the magnitude of the centripetal acceleration?

Accepted Answer

$$a_c = \frac{v^2$}{r}$$

Question 3

A car of mass $$m$$ rounds a flat curve of radius $$r at $$speed $$v. $$What is the minimum coefficient of static friction $$\mu_s$$ required to prevent skidding?

Accepted Answer

$$\mu_s = \frac{v^2$}{g r}$$

Question 4

In uniform circular motion, which of the following always points toward the center of the circle?

Accepted Answer

Centripetal acceleration and net force

Question 5

A ball of mass $$m is $$swung in a vertical circle of radius $$r. $$What is the minimum speed $$v_{min} at $$the top of the circle so that the string remains taut?

Accepted Answer

$$v_{min} = \sqrt{g r}$$

Question 6

If the tension in the cord at the bottom of a vertical circle is calculated for a ball moving at twice the minimum speed required at the top, which equation gives the tension $$T_{bottom}$$?

Accepted Answer

$$T_{bottom} = m \left( \frac{v^2$}{r} + g \right)$$

Question 7

A car is rounding a curve on a flat road. If the tires lose grip and begin to skid, what type of friction is acting and what is the consequence?

Accepted Answer

Kinetic friction; the car is less able to stay on the curve and may skid outward.

Question 8

A 0.50 kg ball is attached to a string and revolves in a horizontal circle of radius 0.60 m at 2.0 revolutions per second. What is the tension in the string?

Accepted Answer

$$T = m \$$omega^2$$ r$$, where $$\omega = 2 \pi f$$

Question 9

Which statement about centrifugal force in uniform circular motion is correct?

Accepted Answer

Centrifugal force is a fictitious force that appears in a rotating reference frame.

Question 10

A car of mass $$m$$ rounds a curve of radius $$r at $$speed $$v. If $$the road is icy and the coefficient of static friction is $$\mu_s = 0.25$$, which of the following is true?

Accepted Answer

The maximum speed before skidding is $$v_{max} = \sqrt{\mu_s g r}$$

Question 11

A mass $$m is $$attached to a string and moves in a horizontal circle of radius $$r on a $$frictionless table. If the maximum tension the string can withstand is $$T_{max}$$, what is the maximum speed $$v_{max}$$ the mass can have?

Accepted Answer

$$v_{max} = \sqrt{\frac{T_{max} r}{m}}$$

Question 12

Which of the following is NOT a consequence of kinetic friction acting when a car skids on a curve?

Accepted Answer

Kinetic friction is greater than static friction, so the car is more stable.

Question 13

A ball of mass $$m is $$swung in a vertical circle of radius $$r at $$constant speed $$v. $$What is the tension $$T_{top} in $$the string when the ball is at the top of the circle?

Accepted Answer

$$T_{top} = m \left( \frac{v^2$}{r} - g \right)$$

Question 14

Which of the following real-world scenarios best illustrates the concept of centripetal force?

Accepted Answer

A car turning around a curve, where friction between the tires and road provides the necessary force.

Question 15

If the net force acting on an object in circular motion suddenly vanishes, what path will the object follow?

Accepted Answer

It will move in a straight line tangent to the circle at that point.

Question 16

A car of mass $$m is $$moving at speed $$v$$ around a flat curve of radius $$r. $$What is the expression for the required net force to keep the car moving in a circle?

Accepted Answer

$$F_{net} = m \frac{v^2$}{r}$$

Question 17

Which of the following statements about uniform circular motion is correct?

Accepted Answer

The speed is constant, but the velocity is continuously changing direction.

Question 18

A ball of mass $$m is $$attached to a string and swung in a vertical circle. At which point is the tension in the string greatest?

Accepted Answer

At the bottom of the circle.

L-10 Uniform Circular Motion: Kinematics and Dynamics

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