energy stores and systems (topic 1). Flashcards
describe how the student could measure the final speed of the ball, just before it hits the ground (4)
- measure the diameter of the ball using a ruler
- drop the ball through a light gate and record the time the ball interrupted the gate
- repeat and calculate the average time
- speed = distance / time
using ideas about forces, explain why the measured value of speed is different to the calculated value (final speed of the ball, just before it hits the ground) (4)
- as the ball accelerates, the air resistance acting on the ball increases
- this reduces the resultant force acting on the ball
- a lower downward resultant force means a lower acceleration
- the measured value of speed will be lower than the calculated value
- the calculated value does not account for air resistance
calculate the speed of the parachutist after they have fallen 60 m
when the parachutist is closer to the ground, they open their parachute, explain how the speed of the parachutist changes between opening the parachute and moments before hitting the ground, use ideas about forces in your answer (4)
- (when the parachute opens) the air resistance acting on the parachutist increases significantly
- there is now an upwards resultant force on the parachutist causing them to decelerate
- as the parachutist slows down, air resistance decreases
- when the air resistance and weight are equal, the parachutist will travel at constant velocity
state the law of conservation of energy (2)
- energy cannot be created or destroyed
- only transferred from one form to another
as the parachutist falls, both the gravitational potential energy store and the kinetic store of the parachutist decrease, energy is still conserved, explain how energy is still conserved
- as the parachutist falls, there is friction between the air and the parachutist and the parachute
- energy is transferred to the thermal energy store of the parachute and parachutist
the gravitational potential energy and the kinetic energy of the roller coaster are both now zero, explain with reference to the conservation of energy how this is possible (when it brakes) (2)
- when the brakes are applied work is done on the system
- the kinetic energy of the rollercoaster is transferred to the thermal store of the brakes
the rollercoaster comes to rest 80 m after passing point B, calculate the average frictional force acting on the rollercoaster to bring it to rest (kinetic energy of the roller coaster is 940,800 J)
the bow stores 170 J of energy, when released, 80 % of the energy is transferred to the kinetic store of the 300 g arrow, calculate the speed of the arrow as it leaves the bow
state the name of the energy store of the cyclist that is decreasing as they cycle (1)
chemical energy store
the cyclist sees an obstacle in the road and needs to stop quickly, describe the energy transfer that takes place between the brakes being applied and the bicycle coming to rest (2)
- kinetic energy of the bike decreases
- energy is transferred to the thermal store of the brakes
which method of energy transfer takes place as the elastic band is being stretched
mechanical
describe the energy transfer that takes place between A and B, you may assume no energy is lost to the surroundings
- gravitational potential energy decreases
- kinetic store increases (or gravitational potential energy is transferred mechanically to the kinetic store of the cart)
explain why the roller coaster is travelling at a lower speed than that calculated in part d -> (calculate the speed of the roller coaster at B) (2)
- not all of the gravitational potential energy at A is transferred to the kinetic store of the cart
- energy is transferred to the thermal store of the surroundings (or energy is lost as heat due to friction between the cart and the track)
500,000 J
