Chapter3
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Which has more momentum, a speeding baseball or an ocean liner at rest in a harbor?
Speeding baseball
A truck moves with a certain momentum. If both its speed and its mass are doubled, how much greater is its momentum?
Four times
If a fast-moving object strikes you, you’ll experience less impact if you can • shorten the time the momentum decreases • increase the time the momentum decreases • either shorten or increase the time, for the result is the same • none of the above
Increase the time the momentum decreases
If your speeding car slams into a haystack and comes to rest, how will the IMPULSE that acts on it compare with slamming into a brick wall and coming to rest?
The amount of impulse will be the same either way (because it’s a matter of force and time)
A fast-moving massive car has a head-on collision with a slow-moving light car. Upon which is the impulse greater?
Impulse is the same on both
A cannon with a long barrel fires a shell faster because the shell experiences a greater • acceleration • impulse • change in intertia • none of these
Impulse
If Superman in space throws a boulder with 10 times as much mass as himself, and the boulder leaves his hands at 100km/h, how fast does superman recoil?
1000km/h
Two identical gliders slide toward each other on an air track. One moves at 2 m/s and the other at 1 m/s. If they stick together, the combination slides at • 0.5 m/s • 1 m/s • 1/5 m/s • 2 m/s
0.5 m/s
Which requires more work, lifting a 25-kg bag of cement 10m vertically, or lifting a 50-kg bag 5m vertically?
Both the same
Which requires more POWER, lifting a 25kg bag of cement 10m vertically in 1 minute, or lifting a 50kg bag 5m vertically in 2 minutes?
25kg bag
Consider two waterfalls, one twice the height of the other. The kinetic energy of each kilogram of water falling to the bottom of the taller waterfall is about • twice and much • four times as much • the same • none of the above
Twice as much
According to the work-energy theorem, in the absence of friction, if you do 100J of work on a cart, you’ll increase it’s kinetic energy by • less than 100J • 100J • more than 100J • 100J squared
100J
An object that has kinetic energy must have • momentum • acceleration • a force applied to it • all of these
Momentum
Consider an ideal pulley system. Pull one end of a rope downward by 1 meter with 50N of force, and you’ll life a 200N load a distance of • 1m • 0.5m • 0.25m • none of these
0.25m
What is the point of bending your knees upon impact of the ground?
To increase the time during which your momentum decreases
Law of Conservation of Momentum
In the absence of an external force, the momentum of a system remains unchanged.
Momentum =
Mass X Velocity
Impulse =
Force X time
T/F: Impulse equals a change in momentum.
True
Work =
Force X Distance
What is the unit for work?
N.m, or J (joule)
Power =
Work done / time interval
An increase in the time it takes for work to be done: increases or decreases power?
Decreases power
T/F: If an object is not moving, no work is being done.
True