Module 3: Chapter 7 - Laws of Motion and Momentum Flashcards
What is momentum?
Momentum is a measure of how difficult it is to stop a moving object.
Momentum = mass x velocity
ρ = mv
What are the units for momentum?
kgms⁻¹ / Ns
What is newtons first law of motion?
An object at rest will stay at rest and an object in motion will remain in motion unless acted upon by an unbalanced force
What is newtons second law of motion?
The rate of change of momentum of an object is directly proportional to the resultant force acting on the object
F = (mv - mu) / t
When m is constant them F = ma
A tennis ball of mass 250g strikes a surface with a velocity of 15ms⁻¹. It rebounds directly backwards with a velocity of 7ms⁻¹. What is the change in momentum?
5.5kgms⁻¹
What is the principle of conservation of linear momentum?
The total linear momentum of a system of interacting bodies is constant, providing no external forces act.
What is a collision?
When objects move together and hit one another
What is an explosion?
Where objects fly apart from one another after initially being at rest
What is a perfectly elastic collision?
A collision in which the objects move in opposite directions after the collision.
* Momentum is conserved
* Total energy is conserved
* Kinetic energy is conserved
What is an inelastic collision?
A collision in which objects stick together after the collision or move in the same direction
* Momentum is conserved
* total energy is conserved
* Kinetic energy is not conserved
What is the equation for kinetic energy in terms of momentum?
What is the equation for impulse?
Ft = mv - mu
I = mv - mu
What is impulse?
The product of the force and the time the force acts, this is equal to the change in momentum
What is the area under a force-time graph?
Impulse
What is the equation for impulse from a force-time graph?
What is the equation for impact force?
Impact Force = (mv - mu) / t
How do safety features help keep passengers safe in the event of a car crash?
In a car crash, safety features help to increase the amount of time over which a collision occurs. This reduces the rate of change of momentum and therefore reduces the impact force experienced. Features include:
* Seatbelts - stretch slightly to prolong the passengers impact time
* Crumple zones - increase collision time
* Airbags - increase collision time and spread force across entire body
A stationary radioactive nucleus of mass M ejects an α particle of mass m at a speed of 2x10⁷ ms⁻¹. Given M = 55m, calculate the kinetic energy of the α particle as a percentage of the final total kinetic energy
98.2%
How do you solve a momentum collision question when the 2 particles move off at an angle to each other?
- Resolve the inital momentum into vertical and horizontal components
- The total vertical and total horizontal components must stay constant before and after the collision
- Use final vertical and horizontal components to find the final momentum
What is newtons third law of motion?
When 2 objects interact, they exert equal and opposite forces on each other
What are the 4 fundamental forces?
- Gravitational
- Electrostatic
- Strong Nuclear
- Weak Nuclear
Explain the interaction between pushing 2 objects together in terms of the 4 fundamental forces.
WHen you push 2 objects together, the contact you feel is due to the electrostatic repulsive forces between the electron clouds around the atomic nuclei in your hands.
