Ch. 2 Check Your Understanding

Question 1

A honeybee leaves the hive and travels a total distance of 2 km before returning to the hive. What is the magnitude of the displacement vector of the bee?

Answer 1

0m

Question 2

Is the average speed of a vehicle a vector or a scalar quantity?

Answer 2

Scalar

Question 3

Two buses depart from Chicago, one going to New York and one to San Francisco. Each bus travels at a speed of 30m/s. Do they have equal velocities?

Answer 3

No

Question 4

Which statement is incorrect?
A) the car traveled around the circular track at a constant velocity.
B) the car traveled around the circular track at a constant speed.

Answer 4

A is incorrect

Question 5

A straight track is 1600m in length. A runner begins at the starting line, runs due east for the full length of the track, turns around and runs halfway back. The time for this run is five minutes. What is the runner’s average velocity and his average speed?

Answer 5

5mins = 300s

Average velocity = displacement/time = 800m/300s = 2.67m/s due east

Average speed = d/t = 2400m/300s = 8m/s

Question 6

The average velocity for a trip has a positive value. Is it possible for the instantaneous velocity at a point during the trip to have a negative value?

Answer 6

Yes

Question 7

At one instant of time, a car and a truck are traveling side by side in adjacent lanes of a highway. The car has a greater velocity than the truck has. Does the car necessarily have the greater acceleration?

Answer 7

No

Question 8

Two cars are moving in the same direction (the positive direction) on a straight road. The acceleration of each car also points in the positive direction. Car 1 has greater acceleration than car 2 has. Which of the following statements is true?
A) the velocity of car 1 is always greater than the velocity of car 2
B) the velocity of car 2 is always greater than the velocity of car 1
C) in the same time interval, the velocity of car 1 changes by a greater amount than the velocity of car 2 does
D) in the same time interval, the velocity of car 2 changes by a greater amount than the velocity of car 1 does

Answer 8

C is correct

Question 9

An object moving with a constant acceleration slows down if the acceleration points in the direction opposite to the direction of the velocity. But can an object ever come to a permanent halt if it’s acceleration truly remains constant?

Answer 9

No

Question 10

A runner runs half the remaining distance to the finish line every 10 seconds. She runs in a straight line and does not ever reverse her direction. Does her acceleration have a constant magnitude?

Answer 10

No

Question 11

The muzzle velocity of a gun is the velocity of the bullet when it leaves the barrel. The muzzle velocity of one rifle with a short barrel is greater than the muzzle velocity of another rifle that has a longer barrel. In which rifle is the acceleration of the bullet larger?

Answer 11

The rifle with the short barrel

Question 12

A motorcycle starts from rest and has a constant acceleration. In a time interval t, it undergoes a displacement x and attains a final velocity v. Then t is increased so that the displacement is 3x. In this same increased time interval, what final velocity does the motorcycle attain?

Answer 12

1.73v

Question 13

An experimental vehicle slows down and comes to a halt with an acceleration whose magnitude is 9.80m/s^2. After reversing direction in a negligible amount of time, the vehicle speeds up with an acceleration of 9.80m/s^2. Except for being horizontal, is this motion a) the same as or b) different from the motion of a ball that is thrown straight upward, comes to a halt, and falls back to earth? Ignore air resistance.

Answer 13

A

Question 14

A ball is thrown straight upward with a velocity v0 and in a time t reaches the top of its flight path, which is a displacement y above the launch point. With a launch velocity of 2v0, what would be the time required to reach the top of its flight path and what would be the displacement of the top point above the launch point? 
A) 4t and 2y
B) 2t and 4y
C) 2t and 2y
D) 4t and 4y
E) t and 2y

Answer 14

B

Question 15

Two objects are thrown vertically upward, first one, and then, a bit later, the other. Is it a) possible or b) impossible that both objects reach the same maximum height at the same instant of time?

Answer 15

B) impossible

Question 16

A ball is dropped from rest from the top of a building and strikes the ground with speed vf. From ground level, a second ball is thrown straight upward at the same instant that the first ball is dropped. The initial speed of the second ball is v0=vf, the same speed with which the first ball eventually strikes the ground. Ignoring air resistance, decide whether the balls cross paths a) at half the height of the building, b) above the halfway point, or c) below the halfway point.

Answer 16

B) above the halfway point

Question 17

What is the difference between distance and displacement?

Answer 17

Displacement is a vector, while distance is not a vector.

Question 18

A jogger runs along a straight and level road for a distance of 8.0km and then runs back to her starting point. The time for this round-trip is 2.0h. Which of the following statements is true?
A) her average speed is 8.0km/hr, but there is not enough information to determine her average velocity.
B) her average speed is 8.0km/hr, and her average velocity is 8.0km/hr.
C) her average speed is 8.0km/hr, and her average velocity is 0km/h.

Answer 18

C is true

Question 19

The velocity of a train is 80.0km/hr, due west. One and a half hours later it's velocity is 65.0km/h, due west. What is the trains average acceleration?
A) 10.0 km/hr^2, due west
B) 43.3 km/hr^2, due west
C) 10.0 km/hr^2, due east
D) 43.3 km/hr^2, due east
E) 53.3 km/hr^2, due east

Answer 19

Average acceleration = change in average velocity/change in t

A = vf-vi /t = 65-80 /1.5 = -10

Negative sign shows that acceleration will be opposite to direction of velocity

C

Question 20

In which one of the following situations can the equations of kinematics not be used?
A) when the velocity changes from moment to moment
B) when the velocity remains constant
C) when the acceleration changes from moment to moment
D) when the acceleration remains constant

Answer 20

C

Question 21

In a race two horses, Silver Bullet and Shotgun, start from rest and each maintains a constant acceleration. In the same elapsed time Silver Bullet runs 1.20 times farther than Shotgun. According to the equations of kinematics, which of the following is true concerning the acceleration of the horses?

Answer 21

A(silver bullet) = 1.20*A(shotgun)

Question 22

A rocket is sitting on the launch pad. The engines ignite, and the rocket begins to rise straight upward, picking up speed as it goes. At about 1000m above the ground the engines shut down, but the rocket continues straight upward, losing speed as it goes. It reaches the top of its flight path and then falls back to earth. Ignoring air resistance, decide which of the following statements is true.

Answer 22

D

Question 23

The top of a cliff is located a distance H above the ground. At a distance H/2 there is a branch that juts out from the side of the cliff, and on this branch a birds nest is located. Two children throw stones at the nest with the same initial speed, one stone straight downward from the top of the cliff and the other stone straight upward from the ground. In the absence of air resistance, which stone hits the nest in the least amount of time?

Answer 23

The stone thrown from the ground