Newton's Law Test Questions- Practice and Review
Newton's Law Test Questions: What You Actually Need to Practice
Most students bomb their Newton's Laws test because they memorize formulas instead of understanding what the laws actually mean. This guide cuts through the nonsense and gives you the practice questions and review strategies that actually work.
Quick Refresher: The Three Laws in Plain English
Before diving into practice questions, make sure you actually know these laws. Not the equations—the concepts.
- First Law (Inertia): Objects sit still or keep moving unless something forces them to change. No force = no change in motion.
- Second Law (F=ma): Force equals mass times acceleration. More mass means more force needed to move it.
- Third Law (Action-Reaction): Every push has an equal and opposite push. Forces come in pairs.
If any of those sound fuzzy, go back to your textbook. The questions below will be useless if you don't get the basics down first.
First Law Practice Questions
These questions test whether you understand inertia and equilibrium.
Question 1
A book rests on a flat table. The book is not moving. What can you say about the forces acting on it?
Answer: The forces are balanced. Gravity pulls down with force = mg, and the table pushes up with an equal normal force. Net force = zero, so no change in motion.
Question 2
A hockey puck slides across frictionless ice. It eventually slows down and stops. Why?
Answer: In reality, it wouldn't slow down on frictionless ice—it would keep sliding forever. In real life, friction and air resistance cause the slowdown. On a test, if they say "frictionless," the puck keeps moving at constant velocity.
Question 3
A passenger in a car that suddenly brakes lurches forward. Explain using Newton's First Law.
Answer: The passenger's body wants to keep moving at the car's original speed. When the car stops, the passenger's body continues forward until something (a seatbelt) forces a change.
Second Law Practice Questions
These questions require calculations. This is where most students lose points.
Question 4
A 5 kg object accelerates at 3 m/s². What net force is acting on it?
Answer: F = ma = (5 kg)(3 m/s²) = 15 N
Question 5
A 10 N force pushes a 2 kg block across a frictionless surface. What is the block's acceleration?
Answer: a = F/m = 10 N / 2 kg = 5 m/s²
Question 6
Two forces act on a 4 kg mass: 8 N east and 6 N north. What is the net force and resulting acceleration?
Answer: Net force = √(8² + 6²) = √100 = 10 N at 36.9° north of east. Acceleration = F/m = 10/4 = 2.5 m/s² in the same direction.
Question 7
A car weighing 1200 kg accelerates from rest to 20 m/s in 10 seconds. What average force was applied?
Answer: First find acceleration: a = Δv/Δt = 20/10 = 2 m/s². Then F = ma = (1200)(2) = 2400 N
Third Law Practice Questions
Students consistently mess up action-reaction pairs. Watch out.
Question 8
A 50 kg student stands on a scale in an elevator. The scale reads 600 N. What is the elevator's acceleration?
Answer: Normal force (scale reading) = 600 N. Weight = mg = (50)(10) = 500 N. Since normal force > weight, the elevator is accelerating upward. Net force = 600 - 500 = 100 N. a = F/m = 100/50 = 2 m/s² upward
Question 9
A bird pushes down on the air with its wings. The air pushes up on the bird. Is this an action-reaction pair from Newton's Third Law?
Answer: Yes. Bird pushes air down (action), air pushes bird up (reaction). These forces act on different objects—that's the key.
Question 10
A 3 kg fish swims forward by pushing water backward. If the water exerts 15 N forward on the fish, what is the fish's acceleration?
Answer: The force on the fish is 15 N forward. a = F/m = 15/3 = 5 m/s² forward
Common Mistakes That Cost Points
- Confusing action-reaction pairs with balanced forces. Action-reaction forces act on different objects. Balanced forces act on the same object.
- Using weight instead of mass. Mass stays constant. Weight changes with gravity. F = ma uses mass in kg.
- Forgetting direction matters. Force and acceleration are vectors. A force of 10 N east and a force of 10 N west cancel out.
- Mixing up mass and weight on free-body diagrams. Weight always points down (mg). Normal force points perpendicular to surfaces.
Quick Comparison: Newton's Three Laws
| Law | Key Equation | Applies When | Common Test Trick |
|---|---|---|---|
| First Law | ΣF = 0 | Object at rest or constant velocity | Forces are balanced but not zero |
| Second Law | F = ma | Net force causes acceleration | Asking for force when given mass and acceleration |
| Third Law | Fab = -Fba | Two objects interacting | Forces on same object instead of different objects |
How to Practice Effectively
Don't just read questions. Work through them with pencil and paper.
- Start with free-body diagrams. Draw all forces acting on an object before solving. Most errors come from missing or duplicate forces.
- Label coordinate axes. Pick a direction for positive (usually the direction of acceleration). Break diagonal forces into components.
- Apply each law separately. Ask: Is net force zero (First Law)? What's the net force and mass (Second Law)? What are the action-reaction pairs (Third Law)?
- Check your answers. Plug numbers back in. Does the acceleration make sense? Are forces balanced?
What Your Teacher Won't Tell You
Tests usually have a pattern. The first few questions check basic F = ma calculations. Middle questions involve multiple forces or angles. The last question often combines all three laws in one scenario.
If you're short on study time, focus on Question 6, 8, and 10 above. They cover vector addition, normal force problems, and Newton's Third Law applications—these show up on nearly every test.
That's it. Go practice.