newtons law, forces, momentum, collisions

when a fielder in cricket catches a fast moving ball he always pulls his hands backwards after the ball enters his hands. explain

• ball hitting hand with high acceleration will exert a large force on him (more likely to hurt)

• this pulls hands backwards to slow the ball allows the change in velocity to occur over a larger distance and time, which reduces the acceleration and force on the hand

when parkour athletes land on the ground, they’re taught to hit the ground and progressively collapse and roll onto the ground. explain this

by collapsing and rolling the time for momentum change is prolonged

as Ft = constant , if t rises then the force on the athlete decreases

point c, this is because the ball must rise to the same vertical height to conserve the original potential energy

Explain why the Zeebee slows down as it rises.

As the Zeebee rises, kinetic energy is converted into gravitational potential energy. This causes its speed to decrease until it reaches zero at the highest point.

At the highest point of its motion, what type of energy does the Zeebee have and why?

The Zeebee has gravitational potential energy because it is at maximum height and its velocity is zero, meaning it has no kinetic energy.

State one reason why the Zeebee might not reach the calculated height in real life.

Energy is lost to air resistance and sound, so not all elastic energy is converted into gravitational potential energy.

Describe one improvement to make measurements of height more accurate.

Use a measuring device with a smaller scale (e.g. metre ruler with mm markings) and repeat trials to reduce random error.

A heavier Zeebee is used. Explain how this affects the height reached if the same elastic energy is stored.

A heavier mass results in a lower height because more energy is required to increase gravitational potential energy, so the same energy results in a smaller height.

in a collision, compare forces experienced by 2 cars

according to newton’s third law, the forces of each car is equal and opposite to the force of the other

if two cars r in contact for 0.01s during a collision, compare impulse experienced by both cars and explain

the impulse for both cars is the same but opposite directions

the impulse is equal to the product of force and time and the force on each car is equal and opposite and the cars are in contact for the same period of time

what safety features do drivers include in their cars to protect them in collisions

• seatbelts,

• airbags and

• crumple zones

• increase the time taken for a passenger’s momentum to change during a collision. Since impulse equals change in momentum, increasing the time reduces the force experienced, thereby reducing injury.