AP®︎ Physics 1: Unit 4 Practice Test

Essential Knowledge: 4.1.A.1

Linear momentum is defined by the equation $\vec{p} = m\vec{v}.$

Essential Knowledge: 4.1.A.2

Momentum is a vector quantity and has the same direction as the velocity.

Essential Knowledge: 4.1.A.3

Momentum can be used to analyze collisions and explosions.

Essential Knowledge: 4.1.A.3.i

A collision is a model for an interaction where the forces exerted between the involved objects in the system are much larger than the net external force exerted on those objects during the interaction.

Essential Knowledge: 4.1.A.3.ii

As only the initial and final states of a collision are analyzed, the object model may be used to analyze collisions.

Essential Knowledge: 4.1.A.3.iii

An explosion is a model for an interaction in which forces internal to the system move objects within that system apart.

Essential Knowledge: 4.2.A.1

The rate of change of momentum is equal to the net external force exerted on an object or system. Relevant equation: $\vec{F}_{\mathrm{net}} = \frac{\Delta\vec{p}}{\Delta t}$

Essential Knowledge: 4.2.A.2

Impulse is defined as the product of the average force exerted on a system and the time interval during which that force is exerted on the system. Relevant equation: $\vec{J} = \vec{F}_{\mathrm{avg}}\Delta t$

Essential Knowledge: 4.2.A.3

Impulse is a vector quantity and has the same direction as the net force exerted on the system.

Essential Knowledge: 4.2.A.4

The impulse delivered to a system by a net external force is equal to the area under the curve of a graph of the net external force exerted on the system as a function of time.

Essential Knowledge: 4.2.A.5

The net external force exerted on a system is equal to the slope of a graph of the momentum of the system as a function of time.

Essential Knowledge: 4.2.B.1

Change in momentum is the difference between a system’s final momentum and its initial momentum. Relevant equation: $\Delta\vec{p} = \vec{p} - \vec{p}_0$

Essential Knowledge: 4.2.B.2

The impulse–momentum theorem relates the impulse exerted on a system and the system’s change in momentum. Relevant equation: $\vec{J} = \vec{F}_{\mathrm{avg}}\Delta t = \Delta\vec{p}$

Essential Knowledge: 4.2.B.3

Newton’s second law of motion is a direct result of the impulse–momentum theorem applied to systems with constant mass. Relevant equation $\vec{F}_{\mathrm{net}} = \frac{\Delta\vec{p}}{\Delta t} = m\frac{\Delta\vec{v}}{\Delta t} = m\vec{a}$

Essential Knowledge: 4.3.A.1

A collection of objects with individual momenta can be described as one system with one center-of-mass velocity.

Essential Knowledge: 4.3.A.1.i

For a collection of objects, the velocity of a system’s center of mass can be calculated using the equation $\vec{v}_{\mathrm{cm}} = \frac{\sum \vec{p}_i}{\sum m_i} = \frac{\sum m_i \vec{v}_i}{\sum m_i}$.

Essential Knowledge: 4.3.A.1.ii

The velocity of a system’s center of mass is constant in the absence of a net external force.

Essential Knowledge: 4.3.A.2

The total momentum of a system is the sum of the momenta of the system’s constituent parts.

Essential Knowledge: 4.3.A.3

In the absence of net external forces, any change to the momentum of an object within a system must be balanced by an equivalent and opposite change of momentum elsewhere within the system. Any change to the momentum of a system is due to a transfer of momentum between the system and its surroundings.

Essential Knowledge: 4.3.A.3.i

The impulse exerted by one object on a second object is equal and opposite to the impulse exerted by the second object on the first. This is a direct result of Newton’s third law.

Essential Knowledge: 4.3.A.3.ii

A system may be selected so that the total momentum of that system is constant.

Essential Knowledge: 4.3.A.3.iii

If the total momentum of a system changes, that change will be equivalent to the impulse exerted on the system. Relevant equation: $\vec{J} = \Delta \vec{p}$

Essential Knowledge: 4.3.A.4

Correct application of conservation of momentum can be used to determine the velocity of a system immediately before and immediately after collisions or explosions.

Essential Knowledge: 4.3.B.1

Momentum is conserved in all interactions.

Essential Knowledge: 4.3.B.2

If the net external force on the selected system is zero, the total momentum of the system is constant.

Essential Knowledge: 4.3.B.3

If the net external force on the selected system is nonzero, momentum is transferred between the system and the environment.

Essential Knowledge: 4.4.A.1

An elastic collision between objects is one in which the initial kinetic energy of the system is equal to the final kinetic energy of the system.

Essential Knowledge: 4.4.A.2

In an elastic collision, the final kinetic energies of each of the objects within the system may be different from their initial kinetic energies.

Essential Knowledge: 4.4.A.3

An inelastic collision between objects is one in which the total kinetic energy of the system decreases.

Essential Knowledge: 4.4.A.4

In an inelastic collision, some of the initial kinetic energy is not restored to kinetic energy but is transformed by nonconservative forces into other forms of energy.

Essential Knowledge: 4.4.A.5

In a perfectly inelastic collision, the objects stick together and move with the same velocity after the collision.