Chapter 4 Part 1

An object is moving at a constant velocity. All but one of the following statements could be true. Which one cannot be true?  

• No forces act on the object.
• Three forces act simultaneously on the object. 
• A single force acts on the object. 
• Two forces act simultaneously on the object.

Which one of the following descriptions violates Newton’s first law of motion?  

• A rabbit’s foot is hanging on a chain from the rearview mirror of a car. As the car accelerates, the rabbit’s foot swings toward the windshield. 
• A child is sitting in the back seat of a car and is not wearing a seat belt. The car is traveling forward, and the driver suddenly applies the brakes. The child flies forward against the rear side of the front seat.
• A small suitcase is at the front of the overhead luggage compartment on an airplane. When the airplane begins its takeoff, the suitcase slides to the rear of the compartment. 
• A glass of water is sitting on a table in the dining car of a train. The train brakes as it nears the station, and the glass slides forward.

A cup of coffee is sitting on a table in a recreational vehicle (RV). The cup slides toward the rear of the RV. According to Newton’s first law, which one or more of the following statements could describe the motion of the RV? (A) The RV is at rest, and the driver suddenly accelerates. (B) The RV is moving forward, and the driver suddenly accelerates. (C) The RV is moving backward, and the driver suddenly hits the brakes.

• A
• B
• C
• A, B, and C

A car has a mass of 1600 kg. It is stuck in the snow and is being pulled out by a cable that applies a force of 7560 N due north. The resistance of the snow and mud also applies a force to the car, which has a magnitude of 7340 N and points due south. What is the acceleration of the car?

• 0.14 m/s² north 
•  4.7 m/s² north 
• 9.3 m/s² south
• There is not enough information to determine the car’s acceleration. 

Two ice skaters, Paul and Tom, are each holding on to opposite ends of the same rope. Each pulls the other toward him. The magnitude of Paul’s acceleration is 1.25 times greater than the magnitude of Tom’s acceleration. What is the ratio of Paul’s mass to Tom’s mass? 

• 0.50
•  0.25 
• 0.67
• 0.80

What is the mass on Mercury of an object that weighs 784 N on the earth’s surface? 

• 118 kg 
• 48.0 kg 
• 80.0 kg 
• There is not enough information to calculate the mass.

The apparent weight of a passenger in an elevator is greater than his true weight. Which one of the following is true? 

• The elevator is either moving upward with an increasing speed or moving upward with a decreasing speed.
• The elevator is either moving upward with a decreasing speed or moving downward with an increasing speed. 
• The elevator is either moving upward with a decreasing speed or moving downward with a decreasing speed. 
• The elevator is either moving upward with an increasing speed or moving downward with a decreasing speed.       

Which one of the following objects is in equilibrium?  

• A race horse taking off at the beginning of a race.
• A projectile as it passes through the topmost point of its trajectory. 
• A brick falling from a bridge. 
• A space probe with its engines shut down, moving through a vast empty region of outer space.

A certain object is in equilibrium. Which one of the following statements is not true? 

• The object has a constant velocity. 
• The object must be at rest. 
• The object has no acceleration. 
• No net force acts on the object.

A certain object is not in equilibrium. Three of the following statements could possibly be true, and one must be true. Which one of the following must be true? . 

•  A net force acts on the object.
• Only three forces act on the object.
• Only a single force acts on the object. 
• Only two perpendicular forces act on the object