1.5.2. Friction
A subsection of Physics, 5054, through 1. Motion, forces and energy
Listing 10 of 40 questions
When a car driver sees an emergency ahead, he applies the brakes. During his reaction time the car travels at a steady speed and covers a distance known as the thinking distance. The braking distance is the distance travelled by the car after the brakes are applied. State the energy change that occurs as the car brakes. shows the speed-time graph of a car. The driver sees the emergency at time t = 0. The total mass of the car is 800 kg. t / s speed m / s Determine the thinking distance, the braking distance, the deceleration of the car during braking, the force provided by the brakes. Using ideas about friction and deceleration, state and explain how the braking distance is affected by using new tyres rather than badly worn tyres, the car skidding on a wet road, the car carrying a heavy load of passengers.
5054_s08_qp_2
THEORY
2008
Paper 2, Variant 0
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The overall stopping distance of a cyclist is made up of two parts, as shown in : • the distance the cyclist travels during the reaction time of the cyclist (the thinking distance) • the distance the cyclist travels after the brakes are applied (the braking distance) thinking distance braking distance overall stopping distance (not to scale) State the energy change that occurs during braking. A ball rolls in front of a cyclist at time t = 0 and the cyclist brakes and comes to rest. shows the speed-time graph for the cyclist. 0.4 0.8 1.2 1.6 2.0 time / s 2.4 speed m / s Using , determine the reaction time of the cyclist. reaction time = Using , calculate the thinking distance. thinking distance = State how the braking distance is found using . On another occasion, the same cyclist travels at an initial speed of 5.0 m / s. A ball rolls in front of the cycle at time t = 0. The cyclist has the same reaction time and the deceleration of the cycle is the same as in . On draw the new speed-time graph for the cyclist. The braking distance is longer when the cyclist stops on a wet road. Explain why. Please for Question 12. shows the hydraulic braking system of the cycle. handle bar pivot oil piston S brake pad piston R F IRUFHIURPF\FOLVW·VKDQG brake lever axle of wheel spinning brake disc (not to scale) The cyclist applies a force on the brake lever. This increases the pressure in the oil by 1.2 × 106 Pa. The cross-sectional area of piston R is 5.0 × 10–5 m2. Calculate the force F applied by the brake lever to piston R. F = The force applied to each of the brake pads is larger than F. Explain why.
5054_s16_qp_21
THEORY
2016
Paper 2, Variant 1
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shows a map of the route taken by a car as it travels from town A to town B. town A town B 5 km Scale: The side of one square is 5 km. N E The journey involves a distance and a displacement. Using the scale on , determine the displacement in travelling from A to B. size of displacement = direction of displacement = State how distance differs from displacement. In some parts of the journey, the car is travelling at a constant speed but is also accelerating. Explain how this is possible. At town B the car makes an emergency stop. The total stopping distance of the car is the thinking distance added to the braking distance. Describe what is meant by the thinking distance. The brakes on the car work badly. This increases the braking distance. State two other factors that increase the braking distance. 1. 2. The mass of the car and driver is 1200 kg. Just before the brakes are applied, the speed of the car is 30 m / s. Calculate the kinetic energy of the car and driver just before the brakes are applied. kinetic energy = The braking force that stops the car is 1800 N. Calculate the deceleration of the car. deceleration = Explain why the temperature of the brakes increases during braking.
5054_s19_qp_22
THEORY
2019
Paper 2, Variant 2
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shows the thinking distance and the braking distance for a car being driven along a dry road and along a wet road at the same speed. thinking distance 18 m dry road 18 m 43 m 60 m wet road braking distance Calculate the total stopping distance for the car on the wet road. distance = Complete the sentence. The thinking distance is the distance travelled between seeing a hazard and Suggest why the thinking distance is the same on both roads. Explain why the braking distance is larger when the road is wet.
5054_s20_qp_21
THEORY
2020
Paper 2, Variant 1
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shows the thinking distance and the braking distance for a car driven at 100 km / h. The car has old, smooth tyres. thinking distance braking distance 21 m 75 m Calculate the total stopping distance for the car. stopping distance = The car is now fitted with new tyres. At a speed greater than 100 km / h, the total stopping distance is the same as in . State and explain the effect that the increase in speed and the use of new tyres have on the thinking distance. effect explanation State and explain the effect that the increase in speed and the new tyres have on the braking distance. effect explanation
5054_s20_qp_22
THEORY
2020
Paper 2, Variant 2
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shows the speed–time graph for a car travelling on a straight horizontal road. speed m / s time / s Describe the motion of the car. Using , calculate the distance travelled by the car during the 24 s of its motion. Show your working. distance = Calculate the average speed of the car during its motion. average speed = A second car travels at a steady speed. It travels the same distance as the first car in the 24 s of the journey. On , draw the speed–time graph for the second car. The thinking distance is the distance travelled by a car between the time that a hazard is seen and the time that the brakes are applied. The braking distance is the distance travelled while the car slows down to rest. Table 7.1 shows the thinking and braking distances for an alert driver when the car travels at different speeds. Table 7.1 speed km / h thinking distance / m braking distance / m Complete Table 7.1. The time it takes for the driver to react to the hazard is constant at different speeds. Explain how the table shows this. State what happens to the thinking distance and the braking distance when the driver is tired. thinking distance braking distance
5054_s22_qp_22
THEORY
2022
Paper 2, Variant 2
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Questions Discovered
40