chapter 9 momentum Flashcards
momentum equation
momentum p = mass (kg) * velocity (ms^-1)
what would happen when a ball(1) of velocity v with mass m hits a stationary ball(2) of the same mass
ball(1) would stop on impact, ball (2) would move off with the same velocity v, conserving momentum
what would happen when a ball(1) of velocity v with mass m hits a stationary ball(2) that is much heavier
ball(1) would rebound off of it, while ball(2) would move only a bit slowly as a response
how is momentum conserved in collisions and explosions
the momentum before is the same as the momentum after
mass before * velocity before = mass after * velocity after
is momentum a vector or scalar
vector, the equation for momentum contains velocity, which is a vector
use the equation ‘mv’ to show conservation of momentum between a ball of velocity v hitting a stationary ball, both have same mass
mv + 0 = mv –> 0 + mv = mv
state newton’s first law - the law of inertia
a body stay at rest, or continue to accelerate at a constant acceleration, unless acted upon by an external force
state Newton’s second law - the law of force
the acceleration of an object is directly proportional to the force applied (F = ma).
how does Newton’s second law apply to momentum
the rate of change of momentum is directly proportional to the force
F = Δp / Δt = ma
Δp = mΔv
what is impulse of a force
the force multiplied by the time the force is applied for, so impulse is equal to the change in momentum
Δp = FΔt
how do you increase impulse
increase the force, or the time it acts for
how are crumple zones in cars used for improved driver safety
they reduce the force on the driver
as momentum is constant, and Δp = FΔt
crumple zones increase the duration of the crash, so change in time increases, but to keep change in momentum constant, the force decreases so the force on the passenger decreases, improving their safety
how do seat belts air bags improve safety
they reduce the force on the driver
as momentum is constant, and Δp = FΔt
seat belts stretch slowly and air bags deflate gradually, increasing how long it takes for a person to come to a halt if the car comes to a halt
how do you get impulse from a force-time graph
the area under a force time graph between 2 points on the X-axis give the impulse
what does area under a graph of force-time give
impulse (change in momentum)
what does the peak of the force-time graph give
maximum deformation of an object
state Newton’s third law
every action has an equal and opposite reaction.
equation of force for free falling object near earth surface
F = m g
m is mass in kg
g is acceleration usually 9.81
what is the equation including work done, change in energy and force
work done ΔE (J) = force (N) * displacement in direction of force Δs (m)
what is the conservation of energy
energy is never created or destroyed, only transferred between different forms and stores of energy
how do you calculate kinetic energy gained
E(K) = 0.5 * mass (kg) * velocity^2
how do you calculate gravitational potential energy
GPE (ΔEgrav) = m (kg) * g (accel = 9.8) * h (metres)
how do you combine kinetic energy with GPE
kinetic energy gained = change in gravitational potential energy
define projectile and give example
object projecting outwards such as a canonball
how do you do calculations for a force acting at angles
how would you do it for a mass mg acting at angle theta
you need to resolve it into vertical and horizontal components, and use the component acting in the direction of the motion
mg cos theta = mg * cos theta
define power
rate at which work is done
rate at which energy is transferred
equations for power
work done / time
P (W) = ΔE (J) / T (secs)
force * velocity
P = force (N) * velocity (ms^-1)
