Force
What is the SI unit of force?
A. Joule
B. Newton
C. Watt
D. Pascal
B. Newton
A book is resting on a table. Which of the following best illustrates Newton’s First Law?
A. The book will slide across the table by itself.
B. The book will remain at rest until a force moves it.
C. The book will fall upward if the table is strong enough.
D. The book is constantly accelerating.
Answer: B ✅
Explanation: Objects at rest stay at rest unless acted upon by an external force. The book remains stationary because no horizontal force is acting on it.
What does Newton’s Third Law of Motion state?
A. An object at rest stays at rest unless acted upon by a force.
B. Force equals mass times acceleration.
C. For every action, there is an equal and opposite reaction.
D. Gravity causes objects to fall.
Answer: C ✅
Explanation: Newton’s Third Law states that forces always come in pairs: if object A exerts a force on object B, then B exerts an equal and opposite force on A.
1. What does Newton’s Third Law of Motion state?
A. An object at rest stays at rest unless acted upon by a force.
B. Force equals mass times acceleration.
C. For every action, there is an equal and opposite reaction.
D. Gravity causes objects to fall.
Answer: C ✅
Explanation: Newton’s Third Law states that forces always come in pairs: if object A exerts a force on object B, then B exerts an equal and opposite force on A.
A book on a table stays at rest until someone pushes it.
A. Newton's 1st Law of Motion
B. Newton's 2nd Law of Motion
C. Newton's 3rd Law of Motion
A.
What kind of physical quantity is force?
Force is a scalar quantity.
Force is a vector quantity.
Force is both a vector quantity and a scalar quantity.
Force is neither a vector nor a scalar quantity.
B. Vector
Because force has both magnitude and direction, and its effects depend on both.
A hockey puck slides on ice and eventually stops. Why does it stop?
A. Because objects naturally slow down.
B. Because an external force (friction) acts on it.
C. Because of its inertia.
D. Because Newton’s First Law does not apply to pucks.
Answer: B ✅
Explanation: Friction is an external force that slows down the puck. Without friction (a nearly frictionless surface), the puck would continue moving indefinitely, illustrating Newton’s First Law.
A 5 kg object is subjected to a net force of 20 N. What is its acceleration?
A.1 m/s²
B.2 m/s²
C.4 m/s²
D.100 m/s²
Answer: C ✅
Explanation: Use
F= ma
20N/5kg= 4m/s^2
A book rests on a table. What is the action-reaction pair?
A. Gravity on the book / book on the table
B. Normal force on the book / gravity on the book
C. Book on table / friction on table
D. Table pushes horizontally / book pushes horizontally
Answer: A ✅
Explanation: The weight of the book (gravity on book) is the action; the gravitational pull of the book on Earth is the reaction. The table provides a separate normal force, another action-reaction pair.
A swimmer pushes water backward, and the water pushes the swimmer forward.
A. Newton's 1st Law of Motion
B. Newton's 2nd Law of Motion
C. Newton's 3rd Law of Motion
C. Newton's 3rd Law of Motion
A box rests on a horizontal surface. The free-body diagram below shows two forces acting on the box:
A downward arrow labeled Weight (W)
An upward arrow labeled Normal Force (N)
Which conclusion can be drawn from this free-body diagram?
A. The box must be accelerating upward.
B. The net force on the box is zero, so it is in equilibrium.
C. The normal force is greater than the weight, so the box moves upward.
D. The forces act in opposite directions, so the box must be moving downward.
A net force of zero means the box is in equilibrium (it is either at rest or moving at constant velocity).
✅ Correct answer: B. The net force on the box is zero, so it is in equilibrium.
Why the other options are wrong:
A: Accelerating upward → would require N > W, which isn’t indicated.
C: Normal force greater than weight → again, not shown.
D: Forces in opposite directions → doesn’t imply motion; net force matters, not just direction.
An astronaut in deep space is floating motionless relative to nearby stars. What will happen if no external force acts on them?
A. They will start moving randomly.
B. They will remain motionless.
C. They will fall toward the nearest planet.
D. They will slowly speed up.
Answer: B ✅
Explanation: Without external forces, an object at rest will remain at rest, demonstrating inertia.
A car has a mass of 1000 kg and accelerates at 2 m/s². What net force is acting on it?
A.500 N
B.1000 N
C.2000 N
D.3000 N
Answer: C ✅
Explanation: Using
F=ma:
𝐹=1000×2=2000N
Two people are playing tug-of-war with a rope. Person A pulls on the rope with a force of 200 N to the right. Person B pulls with an equal force of 200 N to the left. The rope has a mass of 5 kg and is initially at rest.
Question:
What is the tension in the rope?
Which direction will the rope accelerate, if any?
Options:
A. Tension = 200 N, rope accelerates right
B. Tension = 200 N, rope does not accelerate
C. Tension = 400 N, rope accelerates left
D. Tension = 0 N, rope accelerates
✅ Answer: B. Tension = 200 N, rope does not accelerate
Explanation:
The rope pulls equally on both ends, creating a tension of 200 N.
Because the forces are equal and opposite, the net force is zero → rope stays at rest.
Newton’s Third Law explains that each person pulls on the rope, and the rope pulls back with equal force.
A grocery cart accelerates more when you push it harder and accelerates less when it’s loaded with heavy items.
A. Newton's 1st Law of Motion
B. Newton's 2nd Law of Motion
C. Newton's 3rd Law of Motion
B. Newton's 2nd Law of Motion
Do two bodies have to be in physical contact to exert a force upon one another?
A.No, the gravitational force is a field force and does not require physical contact to exert a force.
B.No, the gravitational force is a contact force and does not require physical contact to exert a force.
C.Yes, the gravitational force is a field force and requires physical contact to exert a force.
D.Yes, the gravitational force is a contact force and requires physical contact to exert a force.
Explanation:
Field forces (like gravity, electric, and magnetic forces) act over a distance without physical contact.
Contact forces (like friction, tension, and normal force) require physical contact.
Gravity acts between any two masses regardless of whether they are touching, so it is a non-contact (field) force.
All other options are incorrect because they either claim gravity is a contact force or that physical contact is required, which is false.
Which of the following statements is true about inertia?
A. Inertia is the tendency of an object to resist a change in motion.
B. Inertia is the force that makes objects move.
C. Inertia only applies to moving objects.
D. Inertia disappears in space.
Answer: A ✅
Explanation: Inertia is a property of matter, present in all objects, that resists changes in motion, whether at rest or moving.
Two objects, A (2 kg) and B (4 kg), experience the same net force of 10 N. Which object has greater acceleration?
A.Object A
B.Object B
C.Both the same
D. Cannot determine
Answer: A ✅
Explanation: Acceleration
𝑎=𝐹/𝑚
aa=10/2=5m/s^2, ab=10/4=2.5m/s^2
The smaller mass accelerates more for the same force.
A 0.5 kg ball hits a wall with a force of 20 N. How long does it need to exert this force to achieve an acceleration of 40 m/s²?
A. 0.5 s
B. 0.25 s
C. 1 s
D. 0.05 s
Answer: D ✅
Explanation: a=F/m⇒a=20/0.5=40 m/s²a = F/m \Rightarrow a = 20 / 0.5 = 40\ \text{m/s²}a=F/m⇒a=20/0.5=40 m/s²
Since FFF and mmm already satisfy a=F/ma = F/ma=F/m, the time is arbitrary for the given acceleration, but if we consider impulse, the time is very short for the ball to experience such high acceleration.
A passenger lurches forward when a car suddenly stops because their body tends to keep moving at the original speed.
A. Newton's 1st Law of Motion
B. Newton's 2nd Law of Motion
C. Newton's 3rd Law of Motion
A. Newton's 1st Law of Motion
A student pushes a box with 20 N to the right while friction pushes with 5 N to the left. What is the net force?
A. 25 N left
B. 15 N right
C. 5 N right
D. 20 N left
B — 15 N right
Net force = applied force – friction = 20 N – 5 N = 15 N.
Direction is to the right because the applied force is larger.
A hockey puck slides on a nearly frictionless ice surface with an initial speed of 8 m/s. A small patch of rough ice exerts a constant frictional force of 2 N on the puck. If the mass of the puck is 0.5 kg, how long will it take for the puck to come to rest?
A. 2 s
B. 4 s
C. 8 s
D. 16 s
Answer: ✅ A. 2 s
Explanation:
Newton’s First Law says an object will keep moving unless acted on by an external force. Here, friction is the external force that slows the puck, so we calculate how long it takes to bring the puck to rest.
Which of the following statements about Newton’s Second Law is true?
A. Acceleration depends only on mass.
B. Acceleration depends only on force.
C. Acceleration is directly proportional to force and inversely proportional to mass.
D. Acceleration is always constant.
Answer: C ✅
Explanation: a=F/ma = F/ma=F/m, showing the direct proportionality to force and inverse proportionality to mass.
A person jumps off a 50 kg cart by pushing backward with a force of 100 N for 0.5 s. What is the approximate velocity of the cart immediately after?
A. 1 m/s
B. 2 m/s
C. 5 m/s
D. 10 m/s
Answer: B ✅
Explanation: Impulse J=FΔt=Δp=mΔvJ = F \Delta t = \Delta p = m \Delta vJ=FΔt=Δp=mΔv
Δv=FΔtm=100⋅0.550=1 m/s\Delta v = \frac{F \Delta t}{m} = \frac{100 \cdot 0.5}{50} = 1\ \text{m/s}Δv=mFΔt=50100⋅0.5=1 m/s
✅ Wait carefully: 100 * 0.5 = 50, divided by 50 → 1 m/s
Corrected answer: A. 1 m/s
A passenger lurches forward when a car suddenly stops because their body tends to keep moving at the original speed.
A. Newton's 1st Law of Motion
B. Newton's 2nd Law of Motion
C. Newton's 3rd Law of Motion
A. Newton's 1st Law of Motion