PHYSICS 1A03 Lecture Notes - Lecture 8: Net Force, International System Of Units

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To describe the motion of an object, or a system of objects, in terms of a new quantity, called momentum. To associate changes in the momentum of a system with external forces acting on the system. To model interactions within a system, speci cally collisions, using the law of. To distinguish between the two quantities momentum and kinetic energy, both of which characterize the motion of a system. To identify different types of collisions as elastic or inelastic, and to understand the role of momentum and kinetic energy in modelling these interactions. Momentum is de ned as the product of mass times velocity. It is a vector quantity so it has both a magnitude and a direction. The si units for momentum are kg meters per second. When we consider the sum of all forces acting on an object, this results in an acceleration.

Related Questions

In a collision between an electron and a hydrogen atom, it isuseful to select both objects as the system because which ofthese:

The total momentum of the system does notchange during the collision.

During the time interval justbefore to just after the collision, external forces arenegligible.

The kinetic energy of atwo-object system is nearly zero.

The sum of the final kineticenergies must equal the sum of the initial kinetic energies for atwo-object system.

The forces the objects exert oneach other are internal to the system and don't change the totalmomentum of the system

Two blocks of masses m and 3m are placed on a frictionless,horizontal surface. A light spring is attached to the more massiveblock, and the blocks are pushed together with the spring betweenthem (Fig. P9.9). A cord initially holding the blocks together isburned; after that happens, the block of mass 3mmoves to the rightwith a speed of 2.00 m/s. (a) What is the velocity of the block ofmass m? (b) Find the systemâs original elastic potential energy,taking m = 0.350 kg. (c) Is the original energy in the spring or inthe cord? (d) Explain your answer to part (c). (e) Is the momentumof the system conserved in the bursting-apart process? Explain howthat is possible considering (f) there are large forces acting and(g) there is no motion beforehand and plenty of motionafterward?

Please check my work and if incorrect please provide detailedresponse.
a.) conservation of energy
3m*2+m*v=0
v=-6(m/s) (left)

b.) Energy is conserved
K=((0.350kg)(6^2))/2+((3)(0.350kg)(2^2))/2
K=8.4j
c.) The cord has stored no potential energy in the spring.
d.) There is no potential energy in the spring because thepotential energy in the spring has transferred to kinetic energy ofthe two masses.

e/f/g.)Yes. The two blocks of masses m and 3m are in one isolatedsystem (attached to one another with a spring and pushed together)and the mass of the spring is less than both blocks and is onlyused for storing potential energy.

Good Vibes: Introduction to Oscillations

The conditions that lead to simple harmonic motion are as follows:

There must be a position of stable equilibrium.

There must be a restoring force acting on the oscillating object. The direction of this force must always point toward the equilibrium, and its magnitude must be directly proportional to the magnitude of the object's displacement from its equilibrium position. Mathematically, the restoring force F⃗ is given by ⃗, where is the displacement from equilibrium and k is a constant that depends on the properties of the oscillating system.

The resistive forces in the system must be reasonably small.

Consider a block of mass m attached to a spring with force constant k, as shown in the figure(Figure 1) . The spring can be either stretched or compressed. The block slides on a frictionless horizontal surface, as shown. When the spring is relaxed, the block is located at x=0. If the block is pulled to the right a distance A and then released, A will be the amplitude of the resulting oscillations.

Assume that the mechanical energy of the block-spring system remains unchanged in the subsequent motion of the block.

Part A

After the block is released from x=A, it will

(a) remain at rest

(b) move to the left until it reaches equilibrium and stop there.

(d) move to the left until it reaches x=−A and then begin to move to the right.

The time it takes the block to complete one cycle is called the period. Usually, the period is denoted T and is measured in seconds.

The frequency, denoted f, is the number of cycles that are completed per unit of time: f=1/T. In SI units, f is measured in inverse seconds, or hertz (Hz).

Part B

If the period is doubled, the frequency is

(a) unchanged

(b) doubled

Part C

An oscillating object takes 0.10 s to complete one cycle; that is, its period is 0.10 s. What is its frequency f?

Express your answer in hertz.

Part D

If the frequency is 40 Hz, what is the period T?

Express your answer in seconds.

The following questions refer to the figure (Figure 2) that graphically depicts the oscillations of the block on the spring.

Note that the vertical axis represents the x-coordinate of the oscillating object, and the horizontal axis represents time.

Part E

Which points on the x-axis are located at a distance A from the equilibrium position?

(a) R only

(b) Q only

Part F

Suppose that the period is T. Which of the following points on the t-axis are separated by the time interval T?

(a) K and L

(b) K and M

(d) L and N

(e) M and P

Now assume for the remaining Parts G - J, that the x coordinate of point R is 0.12 m and the t coordinate of point K is 0.0050 s.

Part G

What is the period T?

Express your answer in seconds.

Part H

How much time t does the block take to travel from the point of maximum displacement to the opposite point of maximum displacement?

Express your answer in seconds.

Part I

What distance d does the object cover during one period of oscillation?

Express your answer in meters.

Part J

What distance d does the object cover between the moments labeled K and N on the graph?

Express your answer in meters.

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PHYSICS 1A03 Lecture Notes - Lecture 8: Net Force, International System Of Units

PHYSICS 1A03 Full Course Notes

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