Speed

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Apuntes de la lección

What is Speed?

  • Speed is a measure of the distance an object moves in a certain time.
  • Common units include miles per hour (mph) and kilometres per hour (km/h).
  • In physics, speed is usually measured in metres per second (m/s).
  • Constant speed means the same distance is covered each second (e.g., 30 m/s = 30 m every second).

A person walking at 2.0 m/s and a bee flying at 4.5 m/s, illustrating average speed.

A person walking at 2.0 m/s and a bee flying at 4.5 m/s, illustrating average speed.

Calculating Speed

  • The equation for speed is: Speed = Distance ÷ Time.
  • Example: A car travels 400 m in 20 s → Speed = 400 ÷ 20 = 20 m/s.
  • Always include the correct units (m/s) in your answer.

Calculating Distance

  • Rearrange the speed equation: Distance = Speed × Time.
  • Example: An athlete runs at 8 m/s for 50 s → Distance = 8 × 50 = 400 m.

Calculating Time

  • Rearrange the speed equation: Time = Distance ÷ Speed.
  • Use this when you know distance and speed and need to find time.

Relative Speed

  • The speed of one object relative to another can be found by adding speeds.
  • Example: Car at 30 m/s, train 20 m/s faster → train speed = 30 + 20 = 50 m/s.

Two cars with the same speed but different velocities, illustrating that velocity includes direction.

Two cars with the same speed but different velocities, illustrating that velocity includes direction.

Units and Conversions

  • Speed units: m/s (metres per second), km/h (kilometres per hour), mph (miles per hour).
  • In calculations, ensure distance and time are in compatible units (e.g., metres and seconds).

Worked Examples

  • Cyclist: 120 m in 20 s → Speed = 120 ÷ 20 = 6 m/s.
  • Runner: 1500 m in 500 s → Speed = 1500 ÷ 500 = 3 m/s.
  • Dog walker: 1200 m in 1000 s → Speed = 1200 ÷ 1000 = 1.2 m/s.

Key Points

  • Speed = Distance ÷ Time is the core formula.
  • You can rearrange it to find distance or time.
  • Constant speed means the object covers equal distances in equal time intervals.

Diapositivas

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Preguntas de práctica

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  1. 1.What is speed a measure of?

    Easy
    • AThe distance an object has moved in a certain time
    • BThe time an object takes to move a certain distance
    • CThe force acting on an object
    • DThe mass of an object
  2. 2.Which of the following is the correct equation for speed?

    Easy
    • ASpeed = Distance × Time
    • BSpeed = Distance ÷ Time
    • CSpeed = Time ÷ Distance
    • DSpeed = Distance + Time
  3. 3.An object is travelling at a constant speed of 20 m/s. How far does it travel every second?

    Easy
    • A20 m
    • B10 m
    • C40 m
    • D5 m
  4. 4.A car is travelling at 20 m/s and a train is travelling 10 m/s faster than the car. What is the speed of the train?

    Easy
    • A10 m/s
    • B20 m/s
    • C30 m/s
    • D200 m/s
  5. 5.A cyclist travels a distance of 120 m in 20 seconds. What is the cyclist's speed?

    Medium
    • A6 m/s
    • B2400 m/s
    • C0.17 m/s
    • D100 m/s
  6. 6.A runner travels 1500 m in 500 s. What is the runner's speed?

    Medium
    • A3 m/s
    • B750000 m/s
    • C0.33 m/s
    • D1000 m/s
  7. 7.A sound wave travels 686 m in 2 seconds. What is the speed of sound?

    Medium
    • A343 m/s
    • B1372 m/s
    • C344 m/s
    • D684 m/s
  8. 8.Light travels 4,500,000,000 m in 15 seconds. What is the speed of light?

    Medium
    • A300,000,000 m/s
    • B300,000 m/s
    • C67,500,000,000 m/s
    • D4,500,000,015 m/s

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