<p>For which of the following motions of an object must the acceleration always be zero?
I. Any motion in a straight line
II. Simple harmonic motion
III. Any motion in a circle
a. I only b. II only c. III only d. Either I or III, but not II
e. None of these motions guarantees zero acceleration.</p>
<ol>
<li><p>A rope of negligible mass supports a block that weighs 30 N, as shown above. The breaking strength
of the rope is 50 N. The largest acceleration that can be given to the block by pulling up on it with the
rope without breaking the rope is most nearly
a. 6 m/s2 b. 6.7 m/s2 c. 10 m/s2 d. 15 m/s2 e. 16.7 m/s2</p></li>
<li><p>A ball is thrown straight up in the air. When the ball reaches its highest point, which of the following is true?
a. It is in equilibrium. b. It has zero acceleration.
c. It has maximum momentum. d. It has maximum kinetic energy.
e. None of the above</p></li>
</ol>
<p>For number one the answer is e. I is not true because speed could change. II is not true because direction can change. III is not true because speed and direction can change.</p>
<p>For number two I think you use Newton’s second law. Fnet=ma
Fnet= 50N m= about 3 kg and then you solve for acceleration. Therefore a is e (16.7 m/s/s)</p>
<p>For number there the answer is also e. It’s not in equilibrium because gravity always acts on the object. It has a velocity of zero, but not an acceleration of zero (-9.8), momentum is zero, it has maximum PE, but a KE of zero, so therefore e has to be the right answer.</p>
<p>One quick question- How many hand rules do we need to know for Physics B? My teacher ran out of time to teach magnetics (I know awful, right?) so I learned it out of a review book. I only know three hand rules (right hand rule- pointer= field thumb=velocity and palm= force (same with left for electrons) and thumb= current and fingers wrap around to show the direction of the field.</p>
<p>A sphere of mass ml, which is attached to a spring, is displaced downward from its equilibrium position as
shown above left and released from rest. A sphere of mass m2, which is suspended from a string of length l,
is displaced to the right as shown above right and released from rest so that it swings as a simple pendulum
with small amplitude. Assume that both spheres undergo simple harmonic motion</p>
<ol>
<li><p>Which of the following is true for both spheres?
a. The maximum kinetic energy is attained as the sphere passes through its equilibrium position.
b. The maximum kinetic energy is attained as the sphere reaches its point of release.
c. The minimum gravitational potential energy is attained as the sphere passes through its equilibrium
position.
d. The maximum gravitational potential energy is attained when the sphere reaches its point of release.
e. The maximum total energy is attained only as the sphere passes through its equilibrium position.</p></li>
<li><p>A block attached to the lower end of a vertical spring oscillates up and down. If the spring obeys
Hooke’s law, the period of oscillation depends on which of the following?
I. Mass of the block
II. Amplitude of the oscillation
III. Force constant of the spring
a. I only b. II only c. III only d. I and II e. I and III</p></li>
<li><p>An empty sled of mass M moves without friction across a frozen pond at speed vo. Two objects are
dropped vertically into the sled one at a time: first an object of mass m and then an object of mass 2m.
Afterward the sled moves with speed vf . What would be the final speed of the sled if the objects were
dropped into it in reverse order?
a. vf /3 b. vf /2 c. vf d. 2vf e. 3vf</p></li>
<li><p>A new planet is discovered that has twice the Earth’s mass and twice the Earth’s radius. On the surface
of this new planet, a person who weighs 500 N on Earth would experience a gravitational force of
a. 125 N b. 250 N c. 500 N d. 1000 N e. 2000 N</p></li>
</ol>
<p>oh yeah. I understand that. Thanks for clearing that up. I feel very unprepared for the test. My teacher barely got through half the material this year and I had to self study the rest. The rest of my class is freaking out because they don’t know magnetics/nuclear/electricity/modern at all.</p>
<ol>
<li><p>A - b. is not true as that is the minimum kinetic energy and max potential, c. is wrong because for the spring minimum potential energy is at the bottom of the spring [mgh], d is wrong for the same reason, e is wrong because maximum total energy is also obtained at the top of the spring/highest point of pendulum</p></li>
<li><p>E - for a spring T = 2pisqrt(m/k)</p></li>
<li><p>C - not sure but don’t see how order would matter</p></li>
<li><p>B - F = Gm1m2/r^2; m1 is doubled but r is as well, so now it’s F = 2Gm1m2/4r, so 500/2 =250N?</p></li>
</ol>
<p>EDIT: databox, I said it was wrong because e. says that maximum total energy is ONLY at the equilibrium point; it’s actually also at the point of maximum potential energy, which isn’t the equilibrium point in this case</p>