chapter 9 momentum

Question 1

momentum equation

Answer 1

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

Question 2

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

Answer 2

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

Question 3

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

Answer 3

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

Question 4

how is momentum conserved in collisions and explosions

Answer 4

the momentum before is the same as the momentum after

mass before * velocity before = mass after * velocity after

Question 5

is momentum a vector or scalar

Answer 5

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

Question 6

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

Answer 6

mv + 0 = mv –> 0 + mv = mv

Question 7

state newton’s first law - the law of inertia

Answer 7

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

Question 8

state Newton’s second law - the law of force

Answer 8

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

Question 9

how does Newton’s second law apply to momentum

Answer 9

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

Question 10

what is impulse of a force

Answer 10

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

Question 11

how do you increase impulse

Answer 11

increase the force, or the time it acts for

Question 12

how are crumple zones in cars used for improved driver safety

Answer 12

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

Question 13

how do seat belts air bags improve safety

Answer 13

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

Question 14

how do you get impulse from a force-time graph

Answer 14

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

Question 15

what does area under a graph of force-time give

Answer 15

impulse (change in momentum)

Question 16

what does the peak of the force-time graph give

Answer 16

maximum deformation of an object

Question 17

state Newton’s third law

Answer 17

every action has an equal and opposite reaction.

Question 18

equation of force for free falling object near earth surface

Answer 18

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

Question 19

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

Answer 19

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

Question 20

what is the conservation of energy

Answer 20

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

Question 21

how do you calculate kinetic energy gained

Answer 21

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

Question 22

how do you calculate gravitational potential energy

Answer 22

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

Question 23

how do you combine kinetic energy with GPE

Answer 23

kinetic energy gained = change in gravitational potential energy

Question 24

define projectile and give example

Answer 24

object projecting outwards such as a canonball

Question 25

how do you do calculations for a force acting at angles

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

Answer 25

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

Question 26

define power

Answer 26

rate at which work is done

rate at which energy is transferred

Question 27

equations for power

Answer 27

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

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