Physics: Chapter 8 Flashcards
Define momentum
the mass of an object multiplied by its velocity; momentum = inertia in motion
If a small car and a large car have the same speed, which has more momentum?
large car
If a car doubles its speed, what happens to its momentum?
it doubles
What is equal to change in momentum?
impulse
Why are padded dashboards used?
to delay the time of impact (decreases force of impact by increasing time)
If a cannon fires a cannonball, how does the force on the ball compare to the force on the cannon?
equal and opposite
If you are on ice and throw something, what happens to you?
same force pushes on you in opposite direction
What happens to momentum when the mass is doubled?
(mass x velocity)momentum 2x
Why is the recoil speed of a cannon so much smaller than the speed of the cannonball? When would the speeds be the same?
cannon has larger mass; same speed if they had the equal mass
Why do you put your hand out in front of you to catch a ball?
to delay time of impact
If a car hits another car at rest with the mass and they link together, what is the relationship between the initial speed of the 1st car and the speed of the 2 cars linked together?
half the speed
What exerts the force on a rocket to make it move?
exhaust
If you are in space and you throw something with more mass than you, which will have the greater speed, the object or you?
you
If a 2kg object moves at 6m/s, find its momentum.
6m/s X 2kg = 12kg m/s
If a 6kg ball has 90kg m/s of momentum, what is its speed?
90kg m/s / 6 m/s = 15kg
If a ball moving at 5m/s has a momentum of 60kg m/s, what is its mass?
60kg m/s / 5 m/s = 12kg
When a bug hits the windshield of a moving car, describe the forces, impulses, momentum changes, and accelerations of the bug and the car.
force = equal and opposite momentum = equal and opposite but has more acceleration impulse = equal and opposite
Why do fighter’s ride with a punch?
counteracts the momentum of the punch, reduces force
If a 30kg object moves 500m in 25 seconds, find the momentum.
500m / 25 sec = 20m/s
30kg x 20m/s = 600km m/s
If a 3kg block moving 9m/s comes to a stop in 3 seconds, find the force.
f x 3 = 3(0-9)
f x 3 = -27
f = -9N
If a 12kg object moving at 8m/s hits a 9kg block at rest and they stick together, what is their speed afterwards?
(12 x 8) + (9 x 0) = (12 + 9)VF
96 + 0 = (21)Vf
46 = Vf
If a 30kg object moving at 8m/s hits a 20kg object moving towards it at 6m/s and they stick together, what is their speed afterwards?
(30 x 8) + (20 x -6) = (30+20)Vf
240 + -120 = (50)Vf
120 = 50Vf
24 = Vf
If a 20kg ball moving at 3m/s bounces off a spring at about the same speed it had before in the opposite direction, what is its change in momentum?
~V
(3 - -3) = 6
If a car moving at 57m/s is 5x more massive than the car it hits that is at rest, what is their speed afterwards if they lock together?
~P = M~V
5(57) + 1(0) = (5+1)Vf
285 + 0 = 6Vf
47.5 = Vf
A 45kg girl and a 68kg boy are at rest on roller skates. The girl pushes the boy who moves away at 4m/s. What is the girl’s speed?
M1Vf1 = -M2Vf2
(45 x 0) = - (68kg x 4m/s)
Vf1 = 6.04
