3.1C - Circular Motion (12 Physics)

3.1C - Circular Motion

Qld Syllabus

Objectives

• describe uniform circular motion in terms of a force acting on an object in a perpendicular direction to the velocity of the object

• define the concepts of average speed and period

• solve problems involving average speed of objects undergoing uniform circular motion

• define the terms centripetal acceleration and centripetal force

• solve problems involving forces acting on objects in uniform circular motion.

Centripetal Velocity

Formula

Multiple Choice

When using the term “uniform circular motion,” what do we mean by the term “uniform?”

• The direction of the object’s velocity is constant.

• The net force on the moving object is zero newtons.

• The forces acting on the object are uniformly applied from all directions.

• The motion occurs without the influence of the gravitational force

• The motion of the object is at a constant speed.

Multiple Choice

If an object is moving in uniform circular motion, its period is determined by which one of the following quantities?

• the speed of the object

• the centripetal acceleration of the object

• the number of revolutions the object makes each second

• the time interval for the object to make one revolution

• the displacement of the object

Multiple Choice

A ball moves with a constant speed of 4 m/s around a circle of radius 0.25 m. What is the period of the motion in seconds?

• 0.1

• 0.4

• 0.7

• 1

Multiple Choice

The second hand on a watch has a length of 4.50 mm and makes one revolution in 60.00 s. What is the speed of the end of the second hand as it moves in uniform circular motion?

• 9.42 × 10^–4 m/s

• 2.67 × 10^–3 m/s

• 5.34 × 10^–3 m/s

• 4.71 × 10^–4 m/s

Multiple Choice

Approximately one billion years ago, the Moon orbited the Earth much closer than it does today. The radius of the orbit was only 24 400 km. The orbital period was only 23 400 s. Today, the average radius is 385 000 km; and the present period is 2.36 × 10⁶ s. Assuming that the orbit of the Moon is circular, calculate the ratio of the speed of the Moon in its ancient orbit to the speed that it has today.

• 15.8

• 6.39

• 12.8

• 10.2

Centripetal acceleration

QLD Syllabus

Multiple Choice

For an object in uniform circular motion, which one of the following statements is false ?

• The velocity of the object is constant.

• The magnitude of the acceleration of the object is constant.

• The acceleration is directed radially inward.

• The magnitude of the velocity is constant.

• The velocity is directed in a direction that is tangent to the circular path.

Multiple Choice

A solar-powered car is traveling at constant speed around a circular track. What happens to the centripetal acceleration of the car if the speed is doubled?

• The centripetal acceleration remains the same.

• The centripetal acceleration increases by a factor of 2.

• The centripetal acceleration increases by a factor of 4.

• The centripetal acceleration is decreased by a factor of one-half.

Multiple Choice

A rock is whirled on the end of a string in a horizontal circle of radius R with a constant period T. If the radius of the circle is reduced to R/3, while the period remains T, what happens to the centripetal acceleration of the rock?

• The centripetal acceleration remains the same.

• The centripetal acceleration increases by a factor of 3.

• The centripetal acceleration increases by a factor of 9.

• The centripetal acceleration decreases by a factor of 3.

Multiple Choice

A bicycle racer is traveling at constant speed v around a circular track. The centripetal acceleration of the bicycle is ac. What happens to the centripetal acceleration of the bicycle if the speed is doubled to 2v?

• The centripetal acceleration increases to $$4a_c$$

• The centripetal acceleration decreases to $$0.25a_c$$

• The centripetal acceleration increases to $$2a_c$$

• The centripetal acceleration decreases to $$0.5a_c$$

Multiple Choice

A satellite orbits the Earth in uniform circular motion. What is the direction of centripetal acceleration of the satellite?

• Because the centripetal acceleration is a scalar quantity, it doesn’t have a direction.

• The centripetal acceleration vector points radially outward from the Earth.

• The centripetal acceleration vector points radially inward toward the Earth.

• The centripetal acceleration vector points in the direction of the satellite’s velocity.

Centripetal force

QLD Syllabus

Multiple Choice

The centripetal force is best explained by which of the following statements?

• The centripetal force is the force on an object that is directed radially outward from the center of its orbit.

• The centripetal force is the force on an orbiting object that is directed along a line that is tangent to the circle.

• The centripetal force is the net force acting on an orbiting object that maintains it in uniform circular motion.

• The centripetal force is a fundamental force of nature.

Multiple Choice

Which one of the following forces holds a car on an unbanked curve?

• the vertical component of the normal force acting on the car

• the vertical component of the car's weight

• the horizontal component of the normal force acting on the car

• the horizontal component of the car's weight

Multiple Choice

The earth exerts the necessary centripetal force on an orbiting satellite to keep it moving in a circle at constant speed. Which statement best explains why the speed of the satellite does not change although there is a net force exerted on it?

• The centripetal force has magnitude

  $$\frac{mv^2}{r}$$

• The satellite is in equilibrium.

• The acceleration of the satellite is zero $$ms^{-2}$$

• The centripetal force is always perpendicular to the velocity.

Multiple Choice

A satellite travels at a constant speed in a circular orbit around a planet. Which of the following arrows correctly indicates the direction of the net force on the satellite at the instant shown in the drawing?

Multiple Choice

A bicycle racer is traveling at constant speed v around a circular track. The centripetal acceleration of the bicycle is ac. What happens to the centripetal acceleration of the bicycle if the speed is doubled to 2v?

• The centripetal acceleration increases to 4a_c

• The centripetal acceleration decreases to 0.25a_c

• The centripetal acceleration increases to 2a_c

• The centripetal acceleration does not change