# Urgent

<p>Can someone provide explanations to the CB Physics practice test questions?</p>

<p>Is there a document of all of them somewhere?
If not, I can provide the questions</p>

<p>Provide the question</p>

<p><em>Picture of stupid cannon with no information</em></p>

<ol>
<li>Assume that every projectile fired by the toy cannon shown above experiences a constant net force F along the entire length of the barrel. If a projectile of mass m leaves the barrel of the cannon with a speed v, at what speed will a projectile of mass 2m leave the barrel?</li>
</ol>

<p>The energy at that point is the same (same force etc).</p>

<p>Let v1 = when mass is m
Let v2 = when mass is 2m.</p>

<p>E = 1/2<em>m</em>(v1)^2
E = 1/2<em>(2m)</em>(v2)^2</p>

<p>Energy is the same so..
1/2<em>m</em>(v1)^2 = 1/2<em>(2m)</em>(v2)^2
Masses cancel out.</p>

<p>1/2*(v1)^2 = (v2)^2
sq root both sides.
v2 = v1/sqrt(2)</p>

<p>Or you can just use some sort of common sense..</p>

<p>Velocity has to decrease because mass increased...so it has to be either v/2 or v/sq2..</p>

<p>And enough time spent with physics should indicate that mass isn't unit proportional (don't know if it's the right term) to speed.</p>

<ol>
<li>A child on a swing can greatly increase the amplitude of the swing's motion by "pumping" at the natural frequency of he swing. This is an example of what of the following?</li>
</ol>

<p>a. conservation of momentum
b. newton's first law of motion
c. newton's third law of motion
d. resonance
e. interference</p>

<p>Resonance.</p>

<p>Increased amplitude infers a constructive interference. By definition, the same natural frequency would be resonance.</p>

<p>Thanks!</p>

<p>Can you explain diffraction?</p>

<p>It's the whole concept of how light (a wave) bends when it runs into an obstacle. </p>

<p>Think of the double slit experiment. You have two openings, the light bends into either of the openings. Now you have two "arches" of light. </p>

<p>Since they are at different wavelengths relative to each other (like both arches aren't in identical positions) you'll have different points of constructive and deconstructive which will cause different slits of maximum and minimum brightness.</p>

<p>Thanks yet again!</p>