More P3 Flashcards
Name two safety features that absorb energy in a collision.
Seatbelts, air bags, a crumple zone, and a collapsible steering column.
Describe seatbelts.
They prevent people in the car from being propelled forwards in a crash, but may cause bruising.
Describe airbags.
They cushion the impact for the driver and passengers in the event of a crash.
Describe a crumple zone.
It is a part of the car designed to ‘crumple’ during a collision.
Describe a collapsible steering column.
It absorbs energy and breaks to avoid the driver being impaled during an accident.
What do seat belts, air bags, a crumple zone, and a collapsible steering column all have in common as safety features?
They all change shape during an impact to absorb energy. They protect occupants and reduce the risk of injury during a collision.
Why do seatbelts have to be replaced after a crash?
Because they can be damaged by the forces they experience.
What is a safety cage?
A metal cage that strengthens the cabin section of the car, which prevents the vehicle from collapsing when upside down or rolling.
Do safety cages absorb energy, and why?
No, because they remain rigid to prevent the car collapsing on the passengers.
What do Anti-lock braking systems (ABS) do?
They prevent the tyres from skidding, and work by pumping the brakes on and off automatically. This increases the area of the tyres that is in contact with the road. Friction between the two surfaces is increased and so the braking distance is reduced, meaning that the car is able to stop more quickly.
What does traction control on a car do?
It prevents the car from skidding while accelerating, which helps the driver to get out of a dangerous situation quickly.
What does the force experienced by a passenger during a collision depend upon?
The rate of changes of momentum; the quicker the change in momentum, the greater the force experienced.
How can the stopping forces experienced in a collision be reduced?
By increasing the stopping or collision time, and/or increasing the stopping or collision distance
Why does an increase in the collision stopping time decrease the force?
because driving force= mass x acceleration, and if the collision stopping time is increased, the rate of acceleration is decreased so the force is decreased.
Describe skydiving before the parachute opens.
When the skydiver jumps, they initially accelerates due to the force of gravity. As they fall, they experience the frictional force of air resistance (R) in the opposite direction. At that point, weight (W) is greater than R so they continue to accelerate. As their speed increases, so does the air resistance acting on them. the air resistance increases until it’s equal to W. the resultant force then acting on them is zero so their falling speed becomes constant as the forces are balanced. That is the terminal speed.
Describe skydiving after the parachute opens.
When the parachute is opened, unbalanced forces act again because the upward force of R is greatly increased and is bigger than W. The increase in R decreases their speed; as their speed decreases, so does R. R decreases until it’s equal to W. The forces acting become balanced once again and they fall at a steady speed once more, although slower than before. This is a new terminal speed.
When does the terminal speed occur?
When the drag is equal to the weight of the object.
What is the difference between weight and mass?
Weight is due to the force of gravity on an object, mass is the amount of matter that it contains.
What is the downwards force on earth?
10N
When an object falls at its terminal speed, what happens to its kinetic energy?
It stays the same
What is the GPE of an object?
The energy stored due to its height and its mass.
What has GPE (gravitational potential energy)?
Any object with the potential to fall
What is the link between gravitational potential energy and kinetic energy?
When an object falls, it converts GPE into KE. For example, when a driver jumps off a diving board, when a ball rolls down a hill and when a skydiver jumps out of a plane
What happens to the kinetic energy when the mass of a rollercoaster is doubled?
The kinetic energy also doubles
What happens to the kinetic energy when the speed of a rollercoaster car is doubled?
The kinetic energy quadruples
What is the unit of GPE?
Joules
Why would a man with the same mass as another standing on a lower diving board have more Gravitational Potential Energy (GPE) than the other?
Because the higher man is further from the ground.
What would increasing the gravitational field strength do, and why could this not happen on Earth?
It would increase the gravitational potential energy, but this can’t happen on Earth as gravitational field strength is constant.
As an object falls, the GPE is converted into kinetic energy. GPE=mgh, and KE = 1/2mv^2. What is the final equation if all the GPE is turned into KE.
mgh=1/2mv^2 becomes gh=v^2/2, as the ‘m’ on each side is cancelled.
