SENAPREP
Newton’s Laws of Motion Questions
Chapter: Mechanics | Total Available: 17 Real Questions
A 5 N force is defined when a mass of 10 kg isaccelerated with
Correct Answer
📖 Governing Law / Core Concept
The governing principle is Newton's Second Law of Motion, expressed as:
Where:
F = Force (in Newtons, N)
m = Mass (in kilograms, kg)
a = Acceleration (in meters per second squared, m/s2)
🧪 Step-by-Step Breakdown
Given:
F = 5 N
m = 10 kg
Using the formula:
Rearranging gives:
🔍 Option Analysis
- Option (a): 5.0 cm/s2 = 0.05 m/s2 (Incorrect)
- Option (c): 0.5 cm/s2 = 0.005 m/s2 (Incorrect)
- Option (d): 5.0 m/s2 (Incorrect)
⚡ Mnemonic / Speed-Run
Remember: F = ma is key. Force and acceleration are directly proportional.
6. Visual Suggestion
6. Visual Suggestion
A force diagram showing a 10 kg mass with an arrow indicating a 5 N force applied horizontally, leading to an acceleration vector pointing in the same direction with magnitude 0.5 m/s2.
Verified against NCERT Class IX Physics, Chapter 9 (Force and Laws of Motion).
1 dyne (a unit of force in CGS system) equals to
Correct Answer
📖 Governing Law / Core Concept
1 dyne is defined as the force required to accelerate a mass of 1 gram at a rate of 1 cm/s².
🧪 Step-by-Step Breakdown
Using the unit conversion:
Convert grams to kilograms:
Then substituting:
Convert cm to meters:
Then, using the relationship:
Thus confirming that option (d) is indeed correct.
- Conversion of grams to kilograms: \(1\, \text{g} = 10^{-3}\, \text{kg}\)
- Conversion of centimeters to meters: \(1\, \text{cm} = 10^{-2}\, \text{m}\)
- Newton's second law for unit definitions.
A diagram indicating the relationship between CGS and SI units, showing how dyne converts to kg·m/s² through clear unit conversions.
Verified against NCERT Class XI Physics, Chapter 2 (Units and Measurements).
Weight and mass of an object are defined with Newtons laws of motion. Which among the following is true?
Correct Answer
📖 Governing Law / Core Concept
According to Newton's laws of motion, weight \( W \) is the gravitational force acting on an object, related to its mass \( m \) by the equation:
Where:
- \( W \) = Weight (N)
- \( m \) = Mass (kg)
- \( g \) = Acceleration due to gravity (m/s²)
🧪 Step-by-Step Breakdown
Mass is defined as the measure of the amount of matter in an object. It remains constant regardless of location, thereby acting as a constant of proportionality in the weight equation. Weight, on the other hand, is variable - it depends on gravitational force, which changes with the distance from the center of the Earth and the local gravitational field strength.
To illustrate:
- If weight changes, mass remains the same.
- This confirms that mass is a constant of proportionality, while weight varies.
🔍 Option Analysis
Option (a) incorrectly states that weight is a constant of proportionality. Option (c) is false since mass is indeed a constant of proportionality. Option (d) mistakenly labels weight as a universal constant; however, it varies with gravitational force.
⚡ Mnemonic / Speed-Run
Remember: "Mass is Matter's Measure, Weight Wavers with Gravity."
6. Visual Suggestion
6. Visual Suggestion
A diagram illustrating the relationship between mass and weight, showing a scale with mass on one side and weight measurement on the other, emphasizing that while mass remains consistent, weight fluctuates with different gravitational forces.
📖 Factual Verification & Reference
Verified against NCERT Class IX Physics, Chapter 4 (Force and Motion)
Why a fielder in the ground gradually pulls his hands backward while catching a fast moving cricket ball?
Correct Answer
📖 Governing Law / Core Concept
The principle relevant here is the impulse-momentum theorem, which states:
Impulse is the product of the average force and the time duration over which the force acts.
🧪 Step-by-Step Breakdown
When a fielder catches a cricket ball, he effectively receives momentum from the ball, which is equal to:
where \( m \) is the mass of the ball (in kg) and \( v \) is its velocity (in m/s).
By pulling his hands backward, the fielder increases the time (\( \Delta t \)) over which the ball decelerates to rest. This longer time reduces the average force (\( F \)) experienced, calculated as:
Rearranging gives:
This indicates that increasing \( \Delta t \) (catching time) reduces force \( F \), mitigating injury and improving catching success.
🔍 Option Analysis
- Option B: Incorrect, as increasing the acceleration is undesirable when catching a ball.
- Option C: Incorrect, as velocity is not increased; the goal is to decelerate the ball.
- Option D: Incorrect, as the above explanations suffice.
⚡ Mnemonic / Speed-Run
Remember: More Time = Less Force when catching. This mnemonic highlights the benefit of time during collisions.
6. Visual Suggestion
6. Visual Suggestion
A diagram depicting a fielder catching a ball, showing forces acting on the ball and a timeline indicating increased catching time through a backward motion of hands.
📖 Factual Verification & Reference
Verified against NCERT Class XI Physics, Chapter 5 (Laws of Motion).
Which one of the following statements for second law of motion is NOT correct?
Correct Answer
📖 Governing Law / Core Concept
Newton's Second Law of Motion is succinctly described by the relation:
Here, \( F \) is the net force, \( p \) is momentum, and \( t \) is time.
🧪 Step-by-Step Breakdown
According to Newton's Second Law, force is directly proportional to the rate of change of momentum:
where \( m \) is the mass and \( a \) is the acceleration. Thus, the correct interpretation is that \( F \) relates to \( \frac{dp}{dt} \), not simply \( p \).
Identifying the incorrect statement reveals that momentum \( p = mv \) is not a direct factor in this relationship, hence disproving Option D.
🔍 Option Analysis
- Option A: Correct; \( F \propto a \).
- Option B: Correct; force and acceleration share direction.
- Option C: Correct; the rate of momentum change equals force.
- Option D: Incorrect; force is not proportional to momentum.
⚡ Mnemonic / Speed-Run
Remember: \( F \propto \frac{dp}{dt} \) highlights the relationship between force and momentum change.
6. Visual Suggestion
6. Visual Suggestion
A diagram showing a force vector acting on an object with a visible acceleration vector illustrates the proportional relationships defined by Newton's Second Law. This should depict the direction of force and acceleration clearly.
📖 Factual Verification & Reference
Verified against NCERT Class XI Physics, Chapter 5 (Laws of Motion).
A car has an initial velocity of 12 m/s and is brought to rest over a distance of 45 m. The acceleration of the car is.
1. Correct Answer
Option C is correct. The acceleration of the car is negative, indicating deceleration.
📖 Core Concept
Acceleration is the rate of change of velocity; negative acceleration denotes deceleration.
💡 3. Explanation
❌ 4. Option Analysis
- •Option A: \(+1.6 \, \text{m/s}^2\) suggests acceleration, contradicting the deceleration fact.
- •Option B: It is not a valid notation and doesn't represent a real answer.
- •Option D: \(-0.8 \, \text{m/s}^2\) is insufficient to stop the car within 45 m from 12 m/s.
NDA Speed-Run / Mnemonic Shortcut
To quickly find acceleration when an object is brought to rest, use \(v^2 = u^2 + 2as\).
5. Key Takeaways
Deceleration implies negative acceleration, calculated via \(a = -\frac{u^2}{2s}\) formula.
A block of mass 2.0 kg slides on a rough horizontal plane surface. Let the speed of the block at a particular instant be 10 m/s. It comes to rest after travelling a distance of 20 m. Which one of the following could be the magnitude ofthe frictional force?
Correct Answer
📖 Governing Law / Core Concept
Newton's second law of motion states: F = ma, where F is the net force acting on an object, m is its mass, and a is its acceleration.
🧪 Step-by-Step Breakdown
Given:
- Mass (\(m\)) = 2.0 kg
- Initial Velocity (\(u\)) = 10 m/s
- Final Velocity (\(v\)) = 0 m/s
- Distance (\(s\)) = 20 m
Using the third equation of motion:
Substituting the known values:
Simplifying gives:
Now applying Newton's second law:
The negative sign indicates that the frictional force acts in the direction opposite to the motion.
🔍 Option Analysis
Option (b) 20 N, (c) 40 N, and (d) 50 N are not possible as they do not satisfy the equations derived.
⚡ Mnemonic / Speed-Run
To remember laws of motion: "Force equals mass times acceleration."
📊 Visual Diagram Suggestion:
Visual Suggestion
A force diagram showing the block on a rough surface with arrows illustrating gravitational, normal, and frictional forces acting on it. This would aid in visualizing the situation effectively.
Verified against NCERT Class XI Physics, Chapter 6 (Work, Energy and Power).
A car weighs 1,000 kg. It is moving with a uniform velocity of 72 km/h towards a straightroad. The driver suddenly presses the brakes.The car stops in 0.2 s. The retarding force applied on the car to stop it is:
Solution
Option (d) is correct.
Explanation:
- \( F \) = Retarding Force (N)
- \( m = 1000 \, \text{kg} \)
- \( a \) = Acceleration (m/s²)
- Newton's Second Law \( F = ma \)
- Conversion of units from km/h to m/s
- Acceleration calculation using \( a = \frac{v - u}{t} \)
Illustrate a force diagram showing the car with applied force vectors while braking, highlighting the retarding force direction and magnitude compared to the car's motion.
Verified against NCERT Class XI Physics, Chapter 5 (Laws of Motion)
Which of the following statements give characteristics of contact forces?
1. It appears between an object when it is in contact with some other object.
2. It satisfies the third law of motion.
3. It may appear between a pair of solid and fluid.
Select the answer using the code given below:
Correct Answer
📖 Governing Law / Core Concept
Contact forces arise when two or more objects are in direct physical contact, adhering to Newton's Third Law of Motion, which states that every action has an equal and opposite reaction.
🧪 Step-by-Step Breakdown
- Contact forces exist solely when objects are in contact, confirming statement 1.
- According to Newton's Third Law, interacting bodies exert equal and opposite forces, validating statement 2.
- Contact forces can occur between solids and fluids, as seen in drag and buoyancy forces, supporting statement 3.
🔍 Option Analysis
Options A, B, and C each omit at least one accurate characteristic of contact forces; therefore, they are incorrect.
⚡ Mnemonic / Speed-Run
Remember: "Contact forces act while touching and obey Newton’s law." Use the acronym C-F-N to recall: Contact, Forces, Newton.
6. Visual Suggestion
A diagram illustrating the interaction of two objects exerting contact forces, labeled with action-reaction pairs, forces between solid and fluid, and the types of forces experienced.
Verified against NCERT Class 11 Physics, Chapter 5 (Laws of Motion).