Laws of motion — Practice Quiz

Zero

Step 1: Newton's Second Law states that F_net = ma, where F_net is net force, m is mass, and a is acceleration. Step 2: When the net force equals zero (F_net = 0), the equation becomes 0 = ma. Step 3: Since mass (m) cannot be zero for real objects, acceleration (a) must be zero. Step 4: Zero acceleration means the object maintains constant velocity (which could be zero for objects at rest). Step 5: This connects the second law to the first law, showing consistency in Newton's framework.

Walking on the ground

Step 1: Newton's Third Law states that for every action, there is an equal and opposite reaction. Step 2: When walking, your feet push backward on the ground (action force). Step 3: The ground pushes forward on your feet with equal force (reaction force), propelling you forward. Step 4: A ball rolling down uses gravity (not action-reaction), car acceleration involves force and mass (second law), and a book on table involves balanced forces (first law). Step 5: Walking clearly demonstrates the interaction between two objects with action-reaction force pairs.

kg⋅m/s

Step 1: Momentum is defined as p = mv, where m is mass and v is velocity. Step 2: The SI unit of mass is kilogram (kg) and the SI unit of velocity is meter per second (m/s). Step 3: Therefore, the SI unit of momentum is kg⋅m/s. Step 4: kg⋅m/s² is the unit of force (Newton), N⋅m is the unit of energy or torque, and J/s is the unit of power. Step 5: Understanding units helps verify calculations and ensures dimensional consistency in physics problems.

It falls straight down

Step 1: This demonstrates Newton's First Law of Motion and the concept of inertia. Step 2: The coin initially at rest tends to remain at rest due to its inertia. Step 3: When the paper is pulled quickly, there isn't enough time for friction to accelerate the coin significantly. Step 4: Therefore, the coin maintains its original position and falls straight down into the glass below. Step 5: This classic demonstration shows how inertia prevents objects from immediately responding to forces acting on other objects they're in contact with.