The impulse approximation is used in situations where __________.
a. external forces on the system are present, but they are small compared to the large, brief internal forces between parts of the system
If the quantity Z is conserved for a certain system, during a certain process, that means ____________.
any change in Z for parts of the system during the process is offset by an equal but opposite change for the Z of other parts of the system
The image shows two balls about have a head-on collision. Ball A has a mass m and speed of 2v, whereas ball B has mass 2m and speed v. Our system consists of just the two balls and is isolated from external forces. Just before the collision __________.
the total momentum of the system is zero.
- Because of their masses, speeds, and directions, the two balls have momenta that have equal magnitudes but opposite directions. Thus the total momentum of the system is zero.
Two cars experience a collision on a city road. Both drivers are using their brakes when the cars hit. Which statement is true?
Using the impulse approximation, conservation of momentum can be applied to the very brief time period of the collision itself (giving approximate results).
The collision between the cars involves brief forces that are much stronger than the forces of fri
The change in an object's momentum during a certain time interval is equal to __________.
the net force exerted on the object times the duration of the time interval.
Impulse is defined as a force times a duration that the force is applied. The net impulse is found using the net force on the object times a certain time duration. The impulse-mo
Can an object have more than one momentum at a given moment?
No, an object always has one unique velocity and one unique mass at any given moment.
The momentum of an object is not a basic property of the object. It changes depending on the velocity of the object as well as its mass.
You observe two identical balls of putty headed directly toward each other at the same speed; what can you say about their total momentum?
They have zero total momentum.
They have the same mass, equal speeds, and are moving in opposite directions. Adding their momentum vectors will give a total of exactly zero.
The image shows two balls (1 and 2) that are going to collide as they approach the point marked . Ball 1 has a mass of 2m and speed v, while ball 2 has mass m and speed 2v. Both balls are moving at 45� angles with respect to the vertical. Our system consi
the total horizontal component of the momentum of the system is zero
The magnitude of each ball's momentum is the same and since they have symmetric angles relative to the vertical direction, they will both have the same magnitude x-component, given by Th
If two cars have the same mass and speed they __________.
might have the same momentum but might not
Since momentum is a vector the two cars would also have to have the same direction of motion in order for them to have the same momentum. If they have the same mass and speed but different directions, they would
Momentum __________.
is a vector, with a magnitude and a direction
When working with one-dimensional vectors the direction is sometimes indicated using (+) or (-) signs, but that doesn't apply to 2D or 3D vectors.
In which of these processes is the momentum of the object conserved?
A skydiver (the object) with her parachute deployed falls toward the ground at a steady speed.
Playing in the rain, a little girl tackles a little boy. Just before she tackles him, the boy is running east at 3 m/s and the girl is running south at 4 m/s. After the tackle, the girl holds on and the two slide on the wet grass. Our system consists of j
Somewhere south of east, but we can't be any more specific than that.
The momenta of the two children are directed east and south, meaning the total momentum will definitely be somewhere south of east. However, we do not have the mass of either child so w
During a complex collision between many objects, including object A and object C, the impulse exerted on object A by object C is equal to __________.
Impulse is a vector quantity. Because of Newton's third Law the two objects must exert equal and opposite forces on each other. Since they will do so for equal amounts of time they will exert impulses with equal magnitudes but opposite directions on each
If some quantity, let's call it "Z," is conserved for a certain system, during a certain process, that means __________.
Z for that system does not change in any way during that process.
A conserved quantity's total value for a system does not change at all.
The standard units of momentum are kg*m/s. Which of these is an alternate way to express these units?
N*s
We can see this most directly from the impulse-momentum theorem. We can also see this by expressing N as kg
m/s2 and seeing that if we multiply by s we are back to kg
m/s.
During a large, multi-object collision that involves object C, the change in the momentum of object C is equal to __________.
the net impulse exerted on object C
The momentum of a system is conserved during a certain process only if __________.
no net external force is exerted on the system during that process