### **Topic 1: Force and Newton's Laws**
**1. What is a force?**
A force is a push or a pull acting upon an object, resulting from its interaction with another object. It is a vector quantity, having both magnitude and direction.
**2. State Newton's First Law of Motion.**
An object at rest will stay at rest, and an object in motion will continue in motion with a constant velocity (same speed and same direction) unless acted upon by a net external force. This is also called the law of inertia.
**3. What is an inertial frame of reference?**
It is a frame of reference in which Newton's First Law holds true. It is a frame that is not accelerating; it is either at rest or moving with a constant velocity.
**4. State Newton's Second Law of Motion.**
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The direction of acceleration is in the direction of the net force. Formula: **F_net = m a**
**5. How is mass different from weight?**
* **Mass** is the amount of matter in an object and is a scalar quantity. It does not change with location.
* **Weight** is the force of gravity acting on an object. It is a vector quantity (W = m g) and can change depending on the value of 'g' (e.g., on the Moon).
**6. Why does the value of 'g' vary with location?**
The value of gravitational acceleration 'g' varies due to:
* **Altitude:** 'g' decreases as you move further from the Earth's center.
* **Shape of the Earth:** The Earth is not a perfect sphere, so 'g' is greater at the poles than at the equator.
* **Geological formations:** Dense rock deposits can slightly increase the local value of 'g'.
**7. State Newton's Third Law of Motion.**
For every action, there is an equal and opposite reaction. This means if object A exerts a force on object B (action), then object B simultaneously exerts an equal and opposite force on object A (reaction).
**8. What is meant by "particles in equilibrium"?**
A particle is in equilibrium when the net force acting on it is zero. According to Newton's First Law, this means it is either at rest or moving with constant velocity. ΣF = 0.
**9. What is apparent weight?**
Apparent weight is the force you feel supporting you, like the reading on a scale. It can be different from your true weight (mg) if you are in an accelerating frame (e.g., an elevator).
* **Feeling heavier:** When the elevator accelerates upwards, apparent weight > mg.
* **Feeling weightless:** When the elevator accelerates downwards, apparent weight < mg. True weightlessness occurs when the only force acting is gravity.
**10. Distinguish between static and kinetic friction.**
* **Static Friction:** The friction that acts when there is no relative motion between two surfaces. It can vary from zero up to a maximum value.
* **Kinetic Friction:** The friction that acts when two surfaces are sliding past each other. It is generally constant and less than the maximum static friction.
**11. What is terminal speed?**
Terminal speed is the constant maximum speed reached by an object falling through a fluid (like air) when the upward drag force equals the downward gravitational force, resulting in zero net force and zero acceleration.
**12. What provides the centripetal force for a car going around a banked curve?**
On a banked curve, the centripetal force is provided by the horizontal component of the normal force from the road surface. This is why banked curves are safer at high speeds.
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### **Topic 2: Work and Kinetic Energy**
**1. Define work in physics.**
Work is done when a force causes a displacement of an object. It is calculated as W = F * d * cosθ, where θ is the angle between the force vector and the displacement vector.
**2. When is work done considered positive, negative, or zero?**
* **Positive Work:** When the force has a component in the direction of displacement (0° ≤ θ < 90°).
* **Negative Work:** When the force has a component opposite to the direction of displacement (90° < θ ≤ 180°), like friction slowing an object.
* **Zero Work:** When the force is perpendicular to the displacement (θ = 90°), or when there is no displacement.
**3. State the Work-Energy Theorem.**
The net work done on an object by all the forces acting on it is equal to the change in its kinetic energy. W_net = ΔK = (1/2)mv_f² - (1/2)mv_i²
**4. What is kinetic energy?**
Kinetic energy is the energy an object possesses due to its motion. It is given by K = (1/2)mv² and is a scalar quantity.
**5. How do you calculate work for a varying force?**
For a varying force, work is calculated as the integral of the force with respect to displacement. W = ∫ F(x) dx. Graphically, it is the area under the Force vs. Displacement curve.
**6. Define power.**
Power is the rate at which work is done or energy is transferred. The average power is P_avg = Work / Time. The instantaneous power is P = F * v.
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### **Topic 3: Potential Energy and Conservation**
**1. What is gravitational potential energy?**
It is the energy stored in an object due to its position in a gravitational field. Near the Earth's surface, it is given by U_grav = m g h.
**2. State the Law of Conservation of Mechanical Energy.**
In an isolated system where only conservative forces (like gravity) do work, the total mechanical energy (kinetic + potential) remains constant. K_i + U_i = K_f + U_f
**3. What is elastic potential energy?**
It is the energy stored in a deformed elastic object, like a compressed or stretched spring. It is given by U_el = (1/2) k x², where k is the spring constant and x is the displacement from equilibrium.
**4. Distinguish between conservative and non-conservative forces.**
* **Conservative Force:** The work done by this force is independent of the path taken (e.g., gravity, spring force). It depends only on the start and end points. It allows for the definition of potential energy.
* **Non-Conservative Force:** The work done depends on the path taken (e.g., friction, air resistance). It dissipates mechanical energy as heat/sound.
**5. If friction is present, does the total mechanical energy remain constant?**
No. Friction is a non-conservative force. It does work that dissipates mechanical energy, converting it into thermal energy (heat). The total energy of the universe is still conserved, but the mechanical energy of the system is not.
**6. What information can you get from an energy diagram?**
An energy diagram (potential energy vs. position) shows:
* **Equilibrium Points:** Where the slope (dU/dx) is zero.
* *Stable Equilibrium:* At a minimum in the potential energy curve.
* *Unstable Equilibrium:* At a maximum in the potential energy curve.
* **Turning Points:** Where the total energy line crosses the potential energy curve.
* **Forbidden Regions:** Where the object's kinetic energy would be negative, which is impossible.
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### **Topic 4: Momentum and Collisions**
**1. Define linear momentum.**
Linear momentum (p) is the product of an object's mass and its velocity. It is a vector quantity. **p = m v**
**2. State Newton's Second Law in terms of momentum.**
The net force acting on an object is equal to the rate of change of its momentum. **F_net = dp/dt**. This is the more general form, which also applies when mass changes (like in rockets).
**3. What is impulse?**
Impulse (J) is the product of a force and the time interval over which it acts. It is a vector quantity. It is also equal to the change in momentum of the object. **J = F_avg * Δt = Δp**
**4. State the Law of Conservation of Momentum.**
The total momentum of an isolated system (a system with no net external force) remains constant.
**5. Distinguish between elastic and inelastic collisions.**
* **Elastic Collision:** Both momentum *and* kinetic energy are conserved.
* **Inelastic Collision:** Momentum is conserved, but kinetic energy is not. Some kinetic energy is converted to other forms like heat, sound, or deformation.
* **Completely Inelastic Collision:** A special case of inelastic collision where the two objects stick together after colliding. Maximum kinetic energy is lost.
**6. What is the center of mass?**
The center of mass of a body or a system of bodies is the point where the entire mass of the system can be considered to be concentrated for translational motion. It moves as if all external forces were applied at that point.
**7. How does rocket propulsion work? (Conceptually)**
It works on the principle of conservation of momentum. The rocket engine expels high-speed exhaust gases backwards. To conserve momentum, the rocket gains an equal momentum in the forward direction.
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**Final Tips for Your Viva:**
* **Be Confident:** Speak clearly and confidently.
* **Listen Carefully:** Make sure you understand the question before answering.
* **Use Diagrams:** If allowed, draw a quick diagram to explain your answer (e.g., for forces on a banked curve).
* **Keep it Simple:** The answers provided are accurate and to the point. Use them as a base.
Good luck with your viva! You've got this