AP Physics. Please Help.

Test Preparation AP Test Preparation
1

<p>I dont understand the solutions to these problems in my textbook. Please explain how to arrive at the answer.</p>

<li><p>A cylinder has a volume of 0.2 m^3. It is composed of two different materials, with densities of 1000 kg/m^3 and 300 kg/m^3 respectively. If each of these materials has an equal mass, what is the mass of the cylinder? (B) 30 kg.</p></li>
<li><p>An object is falling from a height of h in a vacuum and reaches a final velocity of v. When the object has fallen a distance of h/2, it’s velocity is (A) v/sqrt(2).</p></li>
<li><p>During the summer, railroad track couplers appear to be touching. During the winter the couplers have a space of .375 m between them. Each railraod track is 3 m long and the linear expansion constant is .005 m K^-1. What is the change in temperature the tracks encounter? (B) 10 degs C.</p></li>
<li><p>A cannon of mass 55 kg fires a projectile, exerting a force of 150 N on the object. The cannon rests on a surface with a coefficient of static friction of 0.4. What is the minimum amount of force the cannon must exert on the object for it to overcome the force of friction? (B) 220 N.</p></li>
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2

<p>For 15..
(Assuming the projectile is fired straight ahead)</p>

<p>The force of gravity acting on the cannon would be Fw = mg
The normal force Fn = Fw since the cannon is sitting on a flat surface
The force of friction Ff is defined to be nuFn, where nu is the coefficient of friction.</p>

<p>For the cannon to overcome the force of friction, it must exert a force grater than nuFn, which is the same as nuFw or nu*mg</p>

<p>(0.4)(55)(9.8) = 216N</p>

3

<h1>3</h1>

<p>v^2 = vo^2 + 2a delta s, where delta s is the displacement (you can google for a derivation of this.. or maybe there's one in your book)</p>

<p>Since the initial velocity is zero.. the equation becomes v^2 = 2adeltas, and v = root(2a delta s)</p>

<p>If you've only travelled half the distance, the equation becomes
v<em>^2 = 2adeltas / 2
v</em> = root(2a delta s) / root(2), or
v* = v / root(2)</p>

4

<p>v<em>^2 = 2adeltas / 2
v</em> = root(2a delta s) / root(2), or
v* = v / root(2)</p>

<p>Why does "root(2a delta s)" = v?</p>

5

<p>v = velocity for going the whole distance</p>

<p>"v^2 = 2adeltas, and v = root(2a delta s)"</p>

6

<p>Oh i get it now.</p>