PHYSICS QuizBowl - Newton's Laws of Motion (DIFFICULT)

Which one of the following is true, according to Newton’s laws of motion?

• (A) A sports utility vehicle (SUV) hits a stationary motorcycle. Since it is stationary, the motorcycle sustains a greater force than the SUV does.

• (B) A semitrailer truck crashes all the way through a wall. Since the wall collapses, the wall sustains a greater force than the truck does.

• (C) Sam (18 years old) and his sister (9 years old) go ice skating. They push off against each other and fly apart. Sam flies off with the greater acceleration.

• (D) Two astronauts on a spacewalk are throwing a ball back and forth between each other. In this game of catch, the distance between them remains constant.

• (E) None of the above is true, according to the third law.

The net external force acting on an object is zero. Which one of the following statements is true?

• The object can only be stationary.

• The object can only be traveling with a constant velocity.

• The object can be either stationary or traveling with a constant velocity.

• The object can only be traveling with a velocity that is changing.

A student decides to move a box of books into her dormitory room by pulling on a rope attached to the box. She pulls with a force of 80.0 𝑁 at an angle of 25.0° above the horizontal. The box has a mass of 25.0 𝑘𝑔, and the coefficient of kinetic friction between box and floor is 0.300. Find the acceleration of the box.

A 10-kg suitcase is placed on a scale that is in an elevator. In which direction is the elevator accelerating when the scale reads 75 N and when it reads 120 N?

• Downward when it reads 75 N and upward when it reads 120 N.

• Upward when it reads 75 N and downward when it reads 120 N.

• Downward in both cases.

• Upward in both cases.

A box rests on the floor of an elevator. Because of static friction, a force is required to start the box sliding across the floor when the elevator is (a) stationary, (b) accelerating upward, and (c) accelerating downward. Rank the forces required in these three situations in ascending order.

• a, b, c

• b, c, a

• c, a, b

• a, c, b

Two objects attract each other with a gravitational force of magnitude 2.00×10−8 𝑁 when separated by 20.0 𝑐𝑚. If the total mass of the objects is 5.00 𝑘𝑔, what is the mass of each?

The drawings show three examples of the force with which someone pushes against a vertical wall. In each case the magnitude of the pushing force is the same. Rank the normal forces that the wall applies to the pusher in ascending order.

• C, B, A

• B, A, C

• A, C, B

• B, C, A

• C, A, B

Three identical blocks are being pulled or pushed across a horizontal surface by a force 𝑭 , as shown in the drawings. The force in each case has the same magnitude. Rank the kinetic frictional forces that act on the blocks in descending order.

• B, C, A

• C, B, A

• B, A, C

• C, A, B

• A, C, B