Q1. Why does a book lying at rest on a table remain at rest?

Background

Topic: Newton's First Law (Law of Inertia)

This question tests your understanding of equilibrium and net force. Newton's First Law states that an object at rest will remain at rest unless acted upon by a net external force.

Key Terms and Formulas:

• Net force (): The vector sum of all forces acting on an object.

• Normal force (): The upward force exerted by a surface to support the weight of an object.

• Weight (): The force of gravity acting downward on the object.

Step-by-Step Guidance

1. Identify the forces acting on the book: gravity pulls downward (), and the table pushes upward (normal force ).

2. Write the equation for equilibrium in the vertical direction: .

3. Since the forces are equal and opposite, the net force is zero (), so the book remains at rest.

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Q2. What is the net force acting on a hockey puck sliding on ice at constant velocity?

Background

Topic: Newton's First Law (Inertia and Equilibrium)

This question tests your understanding of motion at constant velocity and the concept of net force.

Key Terms and Formulas:

• Net force (): The sum of all forces acting on the object.

• Constant velocity: Means acceleration () is zero.

• Newton's First Law: if .

Step-by-Step Guidance

1. Recognize that the puck is moving at constant velocity, so there is no acceleration ().

2. Apply Newton's First Law: If , then .

3. Conclude that the net force must be zero for the puck to continue moving at constant velocity.

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Q3. Why does a book slide forward off a bus seat when the bus stops suddenly?

Background

Topic: Newton's First Law (Inertia)

This question tests your understanding of inertia and how objects respond to changes in motion.

Key Terms and Formulas:

• Inertia: The tendency of an object to resist changes in its state of motion.

• Newton's First Law: Objects in motion stay in motion unless acted upon by a net force.

Step-by-Step Guidance

1. Consider the initial state: The book is moving forward with the bus.

2. When the bus stops, the book is not attached and continues moving forward due to inertia.

3. The book slides off because no net force acts to stop its forward motion immediately.

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Q4. What can you say about the force of gravity acting on a stone and a feather?

Background

Topic: Gravity and Weight

This question tests your understanding of how gravitational force depends on mass.

Key Terms and Formulas:

• Force of gravity ():

• Mass (): Amount of matter in an object.

• Acceleration due to gravity (): on Earth.

Step-by-Step Guidance

1. Recall that gravitational force depends on mass: .

2. Compare the masses: The stone has more mass than the feather.

3. Therefore, the stone experiences a greater force of gravity than the feather.

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Q5. What can you say about the acceleration of gravity acting on the stone and the feather?

Background

Topic: Acceleration due to Gravity

This question tests your understanding of how gravitational acceleration is independent of mass.

Key Terms and Formulas:

• Acceleration due to gravity (): on Earth.

• Newton's Second Law:

• Weight ():

Step-by-Step Guidance

1. Write the formula for acceleration: .

2. Substitute the force of gravity: .

3. Notice that mass cancels out, so both objects experience the same acceleration due to gravity.

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Q6. An astronaut kicks a bowling ball on Earth and on the Moon with the same force. How does the pain in his foot compare?

Background

Topic: Mass vs. Weight, Newton's Second Law

This question tests your understanding of the difference between mass and weight, and how force relates to acceleration.

Key Terms and Formulas:

• Mass (): Amount of matter, does not change with location.

• Weight (): Force due to gravity, changes with .

• Force (): Causes acceleration, .

Step-by-Step Guidance

1. Recognize that the mass of the bowling ball and astronaut is the same on Earth and Moon.

2. The force applied to the ball is the same in both cases.

3. The resistance felt by the astronaut's foot depends on the mass, not the weight, so the pain is the same.

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Q7. A block of mass m rests on the floor of an elevator moving upward at constant speed. What is the relationship between the force due to gravity and the normal force?

Background

Topic: Forces in Equilibrium, Newton's Laws

This question tests your understanding of normal force and weight when an object is moving at constant speed.

Key Terms and Formulas:

• Normal force (): Upward force from the floor.

• Weight (): Downward force due to gravity.

• Equilibrium: when acceleration is zero.

Step-by-Step Guidance

1. Identify the forces: (up) and (down).

2. Since the elevator moves at constant speed, acceleration is zero.

3. Apply equilibrium: .

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Q8. A block of mass m rests on the floor of an elevator accelerating upward. What is the relationship between the force due to gravity and the normal force?

Background

Topic: Forces and Acceleration, Newton's Second Law

This question tests your understanding of how acceleration affects the normal force.

Key Terms and Formulas:

• Normal force (): Upward force from the floor.

• Weight (): Downward force due to gravity.

• Newton's Second Law:

Step-by-Step Guidance

1. Write the force equation: (where is upward acceleration).

2. Rearrange: .

3. Since , is greater than .

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Q9. Consider two identical blocks, one resting on a flat surface, and the other resting on an incline. For which case is the normal force greater?

Background

Topic: Normal Force and Inclined Planes

This question tests your understanding of how the normal force changes with the angle of the surface.

Key Terms and Formulas:

• Normal force (): Perpendicular force from the surface.

• Weight (): Downward force due to gravity.

• Inclined plane:

Step-by-Step Guidance

1. For the flat surface, .

2. For the incline, , where is the angle.

3. Since for , the normal force is less on the incline.

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Q10. Why does a box slide off the back of a frictionless truck bed when the truck accelerates forward?

Background

Topic: Friction and Inertia

This question tests your understanding of how friction affects motion and why objects remain at rest when no force acts on them.

Key Terms and Formulas:

• Friction: Force that opposes relative motion between surfaces.

• Inertia: Tendency to resist changes in motion.

Step-by-Step Guidance

1. Recognize that the box is initially at rest relative to the truck.

2. When the truck accelerates, friction would normally push the box forward.

3. With no friction, there is no force to accelerate the box, so it stays at rest as the truck moves away.

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