Physics - 9203 OxfordAQA

Safety In Public Transport

Bayani Gaba-gaba

A bus pulling away from a stop, a train running between stations and a car on an open road all obey the same short list of rules, and those rules decide something very practical: the length of road a vehicle needs before it can come to rest. That length is not a property of the brakes alone. It is set by the speed, by the mass, by how long the driver takes to respond, and by how much grip the tyres can find on the surface underneath them.

This lesson turns that everyday fact into physics you can calculate. You will see why a vehicle at a steady speed has no resultant force acting on it at all, split the distance needed to stop into two parts that behave in completely different ways, and use the kinetic energy of a moving vehicle to work out how far the brakes must act. By the end you will be able to explain, in numbers rather than opinions, why raising the speed by half can add far more than half to the distance a vehicle needs.

Manufura

  1. When a vehicle travels at a steady speed in a straight line the resistive forces are balancing the driving force.
  2. The greater the speed of a vehicle the greater the braking force needed to stop it in a certain distance. The greater the braking force the greater the deceleration of the vehicle. Large decelerations may lead to brakes overheating and/or loss of control. Students should understand for a given braking force, the greater the speed, the greater the stopping distance.
  3. The stopping distance of a vehicle is the sum of the distance the vehicle travels during the driver’s reaction time (thinking distance) and the distance it travels under the braking force (braking distance). A driver’s reaction time can be affected by tiredness, distractions, drugs and alcohol.
  4. When the brakes of a vehicle are applied, work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the brakes increases.
  5. A vehicle’s braking distance can be affected by adverse road and weather conditions and poor condition of the vehicle. Students should understand that ‘adverse road conditions’ includes wet or icy conditions. Poor condition of the car is limited to the car’s brakes or tyres.

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Takardar Darasi

Ask a passenger how quickly a bus can stop and you will usually be told something about the brakes. Ask a physicist and you get a different answer: the brakes are only one of four things that matter, and for the first part of the manoeuvre they are not doing anything at all. A vehicle carries kinetic energy, and every joule of it has to be transferred somewhere before the wheels stop turning. How far the vehicle travels while that happens is a calculation, and it is a calculation you can do with two equations you already have.

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Nazarin Darasi

Barka da kammala darasi akan Safety In Public Transport. Yanzu da kuka bincika mahimman raayoyi da raayoyi, lokaci yayi da zaku gwada ilimin ku. Wannan sashe yana ba da ayyuka iri-iri Tambayoyin da aka tsara don ƙarfafa fahimtar ku da kuma taimaka muku auna fahimtar ku game da kayan.

Za ka gamu da haɗe-haɗen nau'ikan tambayoyi, ciki har da tambayoyin zaɓi da yawa, tambayoyin gajeren amsa, da tambayoyin rubutu. Kowace tambaya an ƙirƙira ta da kyau don auna fannoni daban-daban na iliminka da ƙwarewar tunani mai zurfi.

Yi wannan ɓangaren na kimantawa a matsayin wata dama don ƙarfafa fahimtarka kan batun kuma don gano duk wani yanki da kake buƙatar ƙarin karatu. Kada ka yanke ƙauna da duk wani ƙalubale da ka fuskanta; maimakon haka, ka kallesu a matsayin damar haɓaka da ingantawa.

  1. A bus travels along a straight, level road at a steady speed. Which statement about the forces on the bus is correct? A. The driving force is greater than the resistive forces. B. The resistive forces are equal to the driving force. C. The resistive forces are greater than the driving force. D. There are no forces acting on the bus. Answer: B
  2. Which statement correctly describes the stopping distance of a vehicle? A. It is the distance travelled while the brakes are acting. B. It is the distance travelled during the driver's reaction time. C. It is the thinking distance added to the braking distance. D. It is the braking distance subtracted from the thinking distance. Answer: C
  3. Which of these increases the thinking distance of a vehicle but has no effect on its braking distance? A. An icy road surface B. Badly worn tyres C. A tired driver D. Poorly maintained brakes Answer: C
  4. A car of mass 1000 kg travelling at 20 m/s is brought to rest by a constant braking force of 5000 N. What is the braking distance? A. 20 m B. 40 m C. 80 m D. 100 m Answer: B
  5. When the brakes of a moving vehicle are applied, which statement is correct? A. The kinetic energy of the vehicle increases and the brakes cool down. B. The kinetic energy of the vehicle decreases and the temperature of the brakes increases. C. The kinetic energy of the vehicle is destroyed by the friction force. D. The kinetic energy of the vehicle is unchanged and only its speed falls. Answer: B

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