chapter 9 momentum Flashcards

1
Q

momentum equation

A

momentum p = mass (kg) * velocity (ms^-1)

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2
Q

what would happen when a ball(1) of velocity v with mass m hits a stationary ball(2) of the same mass

A

ball(1) would stop on impact, ball (2) would move off with the same velocity v, conserving momentum

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3
Q

what would happen when a ball(1) of velocity v with mass m hits a stationary ball(2) that is much heavier

A

ball(1) would rebound off of it, while ball(2) would move only a bit slowly as a response

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4
Q

how is momentum conserved in collisions and explosions

A

the momentum before is the same as the momentum after
mass before * velocity before = mass after * velocity after

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5
Q

is momentum a vector or scalar

A

vector, the equation for momentum contains velocity, which is a vector

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6
Q

use the equation ‘mv’ to show conservation of momentum between a ball of velocity v hitting a stationary ball, both have same mass

A

mv + 0 = mv –> 0 + mv = mv

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7
Q

state newton’s first law - the law of inertia

A

a body stay at rest, or continue to accelerate at a constant acceleration, unless acted upon by an external force

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8
Q

state Newton’s second law - the law of force

A

the acceleration of an object is directly proportional to the force applied (F = ma).

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9
Q

how does Newton’s second law apply to momentum

A

the rate of change of momentum is directly proportional to the force
F = Δp / Δt = ma
Δp = mΔv

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10
Q

what is impulse of a force

A

the force multiplied by the time the force is applied for, so impulse is equal to the change in momentum
Δp = FΔt

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11
Q

how do you increase impulse

A

increase the force, or the time it acts for

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12
Q

how are crumple zones in cars used for improved driver safety

A

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

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13
Q

how do seat belts air bags improve safety

A

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

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14
Q

how do you get impulse from a force-time graph

A

the area under a force time graph between 2 points on the X-axis give the impulse

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15
Q

what does area under a graph of force-time give

A

impulse (change in momentum)

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16
Q

what does the peak of the force-time graph give

A

maximum deformation of an object

17
Q

state Newton’s third law

A

every action has an equal and opposite reaction.

18
Q

equation of force for free falling object near earth surface

A

F = m g
m is mass in kg
g is acceleration usually 9.81

19
Q

what is the equation including work done, change in energy and force

A

work done ΔE (J) = force (N) * displacement in direction of force Δs (m)

20
Q

what is the conservation of energy

A

energy is never created or destroyed, only transferred between different forms and stores of energy

21
Q

how do you calculate kinetic energy gained

A

E(K) = 0.5 * mass (kg) * velocity^2

22
Q

how do you calculate gravitational potential energy

A

GPE (ΔEgrav) = m (kg) * g (accel = 9.8) * h (metres)

23
Q

how do you combine kinetic energy with GPE

A

kinetic energy gained = change in gravitational potential energy

24
Q

define projectile and give example

A

object projecting outwards such as a canonball

25
Q

how do you do calculations for a force acting at angles
how would you do it for a mass mg acting at angle theta

A

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

26
Q

define power

A

rate at which work is done
rate at which energy is transferred

27
Q

equations for power

A

work done / time
P (W) = ΔE (J) / T (secs)

force * velocity
P = force (N) * velocity (ms^-1)