2.6.1 Understanding Relative Motion

Question 1

Understanding Relative Motion

Answer 1

• Although the physics of a system remains the same, its description might change depending on the reference frame.
• The equations , , and relate the motion of an object in two different reference frames. M and T are the two frames, and C is the object of interest

Question 2

Which of the following is not an example of relative motion?

Answer 2

A plane is traveling at a speed of 500 mi / h. A daredevil is hanging onto one wing of the plane. The plane drops a package. The person flying the plane calculates the velocity of the package. The daredevil also calculates the velocity of the package.

Question 3

Relative motion is the motion of _____________.

Answer 3

an object as described using two different reference frames or coordinate systems

Question 4

A physicist on a train moving at 10 m / s observes a ball moving at 2 m / s in the same direction as the train’s movement. Suppose someone standing still, to the side of the passing train, observes this event. A third person, in a car traveling at 5 m / s in the same direction as the train, also observes the event. Which of the following statements about the velocity of the ball is correct?

Answer 4

• The person in the train can correctly state that the ball is moving forward at 2 m / s.
• The person standing still can correctly state that the ball is moving at 12 m / s.
• The person in the car can correctly state that the ball is moving forward at 7 m / s.

Question 5

The compass of an airplane indicates that it is flying north at 450 mi/h. The wind velocity is 50 mi/h from the east to the west. The velocity of the airplane relative tot he wind is v A,W. The velocity of the airplane relative to the Earth is v A, E. The velocity of the wind relative to the Earth is v W, E. Which of the following statements is not correct

Answer 5

In the reference frame of the wind the plane’s motion shifts toward the west.

Question 6

The compass of an airplane indicates that it is flying south at 150 mi/h. There is a constant 40 mi/h wind blowing the airplane west to the east. The velocity of the airplane relative tot he wind is v A,W. The velocity of the airplane relative to the Earth is v A, E. The velocity of the wind relative to the Earth is v W, E. Given this information, what is the correct description for v A, W

Answer 6

v A,W = 155 mi/h in the SW direction

Question 7

A boat is observed by a person standing on the opposite bank of a river. The boat crosses the river with a speed relative to the observer of 15 m/s. The river has a constant downstream velocity of 8 m/s. What is the magnitude of the velocity of the boat relative to the river? Also, find the value of theta

Answer 7

v B, R = 17 m/s

theta = 28 degrees

Question 8

A jet is observed by two people. One person is standing in reference frame Q. A second person, in reference frame Q’, that moves at a constant velocity, v, to the right. At t = 0, Q’ is at the same location as Q. Which of the following statement about this even is not correct?

Answer 8

The position of the jet observed in reference frame Q′ equals the position of the jet observed in reference frame Q plus v.