Physics Mechanics Essentials: Laws of Motion Quiz Quiz

Explore foundational concepts from Newton's laws, force interactions, friction, and dynamics with this mechanics essentials quiz. Sharpen your understanding of the core principles that govern motion and force in classical physics.

1. Newton's First Law Application

   If a hockey puck slides on perfectly smooth ice with no external forces acting upon it, what will happen to its state of motion according to Newton’s first law?

   1. It will continue moving at a constant velocity indefinitely.
   2. It will gradually speed up.
   3. It will immediately stop.
   4. Its direction will suddenly change.

   Explanation: Newton’s first law states that an object in motion will remain moving at constant velocity unless acted upon by an external force. The puck will not speed up (option B) or immediately stop (option C) since there is no force to change its motion. The direction will not change (option D) because a change in direction requires a force to act upon it.

2. Identifying the Action-Reaction Pair

   When you jump off a small boat onto a dock, the boat moves backward. What is the correct action-reaction force pair in this scenario according to Newton’s third law?

   1. The boat pushing water and water pushing the boat.
   2. Gravity pulling you down and you pushing the dock.
   3. Your feet pushing the boat backward and the boat pushing you forward.
   4. Your weight and the dock’s support force.

   Explanation: Newton’s third law states that for every action, there is an equal and opposite reaction. When you push your feet against the boat (action), the boat pushes you forward (reaction). The other options describe forces present but not true action-reaction pairs: option B refers to support forces, option C to gravity and a normal force, and option D to forces during rowing, not jumping.

3. Friction Force Example

   A box rests on a flat surface and does not slide when a small horizontal push is applied. Which force is preventing the box from moving?

   1. Normal force
   2. Gravitational force
   3. Kinetic friction
   4. Static friction

   Explanation: Static friction resists initial motion and keeps the box at rest when a small force is applied. Kinetic friction (option B) only comes into play when the box is already moving. The normal force (option C) acts perpendicular to the surface, supporting weight, while gravitational force (option D) pulls the box downward but does not prevent horizontal movement.

4. Unit of Force Recognition

   Which of the following is the correct SI unit of force in mechanics?

   1. Joule
   2. Pascal
   3. Newton
   4. Watt

   Explanation: The SI unit of force is the Newton, which measures the amount of force required to accelerate a 1 kg mass by 1 m/s^2. Joule (option B) is a unit of energy, Watt (option C) measures power, and Pascal (option D) is a unit for pressure. These other units, while essential in physics, are not used to quantify force.

5. Second Law Calculation Scenario

   A 2 kg cart accelerates at 3 m/s² when pushed. What is the net force acting on the cart according to Newton’s second law?

   1. 5 N
   2. 1.5 N
   3. 6 N
   4. 0.67 N

   Explanation: Newton’s second law states that force equals mass times acceleration (F = ma), so 2 kg x 3 m/s² = 6 N. The other options are either incorrect calculations (option B: 2/3, option C: arbitrary, option D: 2/3) and do not match the product of mass and acceleration for this scenario.