Untitled Flashcards Set

                                    PHYSICS 6-10

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Chapter 6

MOMENTUM – INERTIA IN MOTION

Definition : Momentum is a property of moving objects (VECTOR)

                                                Formula: P = m x v

Where : p = momentum (kg x m/s)

              M = mass (kg)

              V = velocity (m/s)

A moving object has :

-       Momentum

-       Kinetic energy

-       Speed

Questions :

1)    A larger heavier object moving at the same speed as a smaller one has more momentum (Momentum depends on mass and velocity. Because the larger object has more mass but the same speed, its momentum is greater)

2)    If two objects have the same mass, the faster moving object has more momentum (Momentum depends on mass and velocity. If both objects have the same mass, the one with the higher velocity has more momentum because momentum increases with speed)

3)    If you double an objects speed its momentum : Doubles

Impulse – “What changes Momentum” ?

Definition : Impulse is what changes an object’s momentum 

                                    Formula : J= F x t

Where : J = impulse ( N x s)

             F = force (N)

             T = time duration of force applied (a)

Impulse – momentum relationship: J = △p of F x t = △ (m.v)

Questions :

1)   If a force Is applied for twice the time impulse : Doubles

2)   If you push an object with twice the force for the same time, its change in momentum : Doubles

Impulses in Real life:

            Increasing momentum:

                        Exp : A golfer follows through after hitting the ball to maximize force and time.

            Decreasing momentum over a long time (Reduces impact for)

                        Exp; Benging your knees when landing a jump.

                                 Catching a ball by moving your hands backwards

            Decreasing Momentum over a short time (increases force)

                        Exp: A karate chop breaking board

                                Punching someone very close to you in the face

Questions :

1)    If a dish falls what happenes: it has the same change in momentum regardless if it lands on a carpet or a hard force but the force of impact is lower if it lands on on the carpet because it is soft.

Conservation of Momentum – “Momentum stays the same “

 Law : If not external force acts on a system, momentum before and after remains the same.

                                    Epf = Epi

·       This means total momentum is conserved in a closed system.

·       Example:
A gun and bullet have zero momentum before firing. After firing, the forward momentum of the bullet is equal to the backward momentum of the gun.

Collision – “Momentum Before = Momentum after”

            Momentum is always conserved in collisions, but there are two types:

1. Elastic Collisions

   • Objects bounce off each other.

   • No energy is lost.

   • Example: Two billiard balls colliding.

2. Inelastic Collisions

   • Objects stick together.

   • Some energy is lost as heat or deformation.

   • Example: Two cars crashing and staying together.

Questions :

1)    A moving freight car collides and couples with a stationary one. What happens to speed?

• It halves → ✅ Correct answer!

2)    A 5kg fish moving at 1 m/s swallows a 1kg fish at rest find the final velocity

How to : 5 x 1 + 1 x 0 = 5 + 1

                        5 = 6y

                   5/6 = 0.38 m/s

3 ) what if a small fish moves to the left at 4 m/s?

                                    (5 x 1) = (1 x -4) = (5+1)

                                                5  – 4

                                                1 = 6y

                                                1/6 = 0.17

Chapter 7 Energy

WORK

Definition: Work= force x distance (

            Formula : W= Fd

            Si unit : Joule (j)

Questions :

·        

• If you push against a stationary wall, do you do work? No, because the wall does not move; work requires displacement.

• A weightlifter holds a barbell overhead for a minute. Is work done? No, because there is no movement in the direction of the applied force.

• If you lift a barbell twice as heavy the same distance, how much more work is done? Twice as much because work is directly proportional to force.

• If you push a cart twice as far with the same force, how much more work is done? Twice as much because work depends on both force and distance.

3.     Power

Definition : power is the rate at which work is done (P= W/t)

• SI Unit: Watt (W), where 1 W = 1 J/s.

• Explanations:

  • Do you do more work running up stairs vs. walking? No, the total work is the same, but running takes less time, meaning more power is used.

  • If an engine delivers twice the power, does it do twice the work or the same work in half the time? The same work in half the time because power is inversely related to time.

3. Mechanical Energy

• Definition: Energy due to position or motion (E).

• SI Unit: Joule (J).

• Forms:

·        

• Kinetic Energy (KE): Energy of motion (KE = 1/2 mv²).

  • If speed doubles, what happens to KE? KE quadruples because velocity is squared in the equation.

• Potential Energy (PE): Stored energy due to position (PE = mgh).

  • If a car is twice as heavy, what happens to PE? PE doubles because mass is directly proportional to potential energy.

  • If height is doubled, what happens to PE? PE doubles because height is directly proportional to PE.

4. Work-Energy Theorem

• Definition: The net work done on an object results in a change in its kinetic energy (W_net = ΔKE).

• Explanations:

  • If you push a crate with 100 N across 10m, with 70 N friction, how much KE does the crate gain? 300 J, because net work done is (100 N - 70 N) × 10m.

  • If a car's speed is doubled, how does stopping distance change? Stopping distance quadruples because kinetic energy depends on the square of velocity.

5. Conservation of Energy

• Definition: Energy cannot be created or destroyed, only transformed.

• Explanations:

  • A drawn bow has 50 J of PE, but the shot arrow has 40 J of KE. Where did the 10 J go? Lost to friction, sound, or heat.

  • A circus diver’s PE converts into KE as he falls. Energy transitions from stored gravitational potential energy to motion.

  • Roller coaster energy transitions: PE at the top is converted into KE at the bottom and back into PE at the next peak.

6. Efficiency

• Definition: Efficiency measures how much useful work is obtained from a given input (Efficiency = Useful work output / Total energy input × 100%).

• Explanations:

  • If a machine puts out 60 J of useful energy for every 100 J input, what is its efficiency? 60% because efficiency is calculated as (60 J / 100 J) × 100%.

  • If a machine is 30% efficient, how much energy is wasted? 70% because only 30% is converted into useful work.

7. Momentum vs. Kinetic Energy

• Momentum (p): p = mv (vector, direction matters, can cancel out).

• Kinetic Energy (KE): KE = (1/2)mv² (scalar, always positive, cannot cancel out).

• Explanation:

  • Momentum is conserved in collisions where direction plays a role.

  • Kinetic energy can change into other forms of energy but remains a scalar value.