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Physics 21 Spring 2012 Test 2 (4 pages)
Name: March 7, 2012 Total Score: 1ZO /120__
Your solutions must begin with any of the following Starting Equations (or their y-equivalent)
X= Xq + Voyt +5 at? Vy = Vox + ayt Vg? = Vox? +2 A(X — Xp)
“ we
LE, = may fs SMsN Fi = Ba a=
K = ton? w= iF ar we=F-d AK = Wher
1 au
AU=—W Uyrav = MYgy spring = 5 kx? R=-3,
> ; GmM
EB o=K+U Ep -E, =Worner Fe = U,=-—
~ os 2 ag > = = a 7
p=me Pret = J=SFat Pp — Py = Jext
A! (3) A particle is moving along the x-axis under the influence of one conservative force £.= - cx where ¢
is a positive constant. At time zero il starts form rest at x-+B. Which is false?
A) The speed of the particle is zero if x=0
B) The potential energy is minimum if x-0
C) The particle has its highest kinctic energy if x=0.
D) At time zero, the potential energy cquals the mechanical energy.
: : a A B : :
x 2.65) The potential energy of a diatomic molecule is given by U = 7 pe where r is the separation and
A and B are positive constants. The radial component of the force is
12A 6B 6B 12A 114 5B 13A 7B
NR=Ta 77 B) R= ; C) R= DR=a- aT
B 3. (5) A space station orbits Earth as a satellite 100km above Karth’s surface, What is the net force on an
astronaut at rest inside the space slalion?
A) equal to her weight on Earth B) a little less than her weight on Earth
C) less than half of her weight on Earth D) zero
2D 4. (5) The mass of a certain planet is two times the mass of the Earth, Its radius is twice the radius of the
earth. The free fall acceleration on this planet is:
A)4g B)2g Cg DD) 4s
D 5. (5) Two objects undergo a collision which we know to be inelastic. We can conclude:
A) The objects stick together. B) The linear momentum is not conserved.
C) The objects must change direction. D) The mechanical energy changes.
Cc 6. (5) A baseball initially traveling with speed Vj in the positive y-direction is hit by a bat, which changes
—— ig Pp g
the ball’s velocity to V- as shown in the figure. The impulse delivered to
the ball by the bat has x-component and y-component. .
A) positive, positive B) negative. negative Vy
C) positive, negative D) negative, positive y-component i >.
x
3970 points for this page
Physics 21 Test 2 Spring 2012 1
7)(30) A coffeeshop has a highly polished
(frictionless) bar which is attached to a wall. The
carpenters who installed the bar used a faulty level,
and the bar makes an appreciable (but unknown) angle
with respect to the horizontal. Drinks are delivered by
pressing a mug of mass Af against a massless spring,
with force constant &, and then releasing it.
One day, a new server compressed the spring a
distance d with a mug, and the mug flew olf the bar’s
end after being released from rest. The mug was at
height /Z above the floor when it was released, and hit
the floor at horizontal distance L from its starting
place. Throughout its motion, ceiling fans created a constant downward blowing lorce of magnitude B on the
mug.
Derive an aa for the speed with which the mug hits the floor, in terms of relevant system paramctcrs
-E;= é W Ob arn
= JA ((gr@H + £ed?)
XS $Di30 points for this page
Physics 21 Test 2 Spring 2012 2
