Download Solutions to Midterm 2 - University of Utah Physics

1'11\ sics 221 () Name: Ju~t/ It)
Fall 2012 - NO\ ember 2
D'H id ,\ilion
Exam 2
1
Fi."d 10/
Vnid: _ _ _ _-:--_ _ _ _ _ _ _ _ _ __
Discussion TA: Bryant
Justin
Will
Yuan
SHOW ALL WORK!! Place a circle or box around each answer: SpecifY units for each answer. Report all numbers to two significant figures. Circle all that apply!
A. [5 pts.} Which ofthe following is always true in a collision between 2 objects. Circle the correct answer.
qw Total linear momentum is conserved. Total kinetic energy is conserved.
Ifthe second object is at rest initially, the object that collides with it will be at rest after the collision.
None of the above.
(c) (d) B. [5 pts.} A skier skis down a smooth (Le., frictionless) hill that has a constant slope. Circle which of the following
may be true.
~
The work done by gravity is positive.
The work done by gravity equals the change in the total energy. Linear momentum is conserved. D{. skrer­
Power is constant. 0 ~ &~,t ~,....
None of the above.
(c) (d) (e) C. [5 pts.] A fixed 3.5 kg block is held in place by a horizontal rope while it sits on a conveyor belt moving at a
constant speed of 0.50 mls relative to a stationary observer. If the coefficient of kinetic friction is 0.40, calculate
the average power (in watts) generated by the frictional force.
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Pin sics 2210
D:nid Ailion
Fall 2012 - Nmcmh<.'r 2
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Name: _Tu_Ll._"_rh....:..
Discussion TA: Bryant
Will
Justin
1
Exam 2
Unid: _ _ _ _...,..-_ _ _ _ _ _ _ _ __
Yuan
SHOW ALL WORK!! Place a circle or box around each answer. Specify units for each answer. Report all numbers to two significant figures. Problem 1 - Continued
D. [5 pis.] Two clowns are launched vertically from the same spring-loaded circus cannon with the spring
compressed the same distance each time. Clown A has a mass of 40 kg and clown B has a mass of 60 kg.
Calculate the ratio oftheir speeds (VA/VB) at the instant the spring passes its unstretched position.
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[5 pts.] A ball of mass mB is released from rest and acquires a velocity of magnitude VB before hitting the ground.
If the mass of the earth is ME. calculate the ratio ofthe magnitude ofthe impulse delivered to the earth to the
magnitude of the impulse delivered to the ball.
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Vnid: ________"'--___________________
Discussion TA: Bryant
Justin
Will
Exam 2
Yuan
2
SHOW ALL WORK!! Place a circle or box around each answer. Specify units for each answer. Report all numbers to two significant figures. A bullet of mass m = 0.015 kg is shot vertically upward in a long rough tube of length 300 m. Due to contact with the inside ofthe tube, it experiences a constant frictional force f= .07 N. The bullet has an initial speed of 80 mls. (a)
(b)
[15 pts.} How high up the tube does the bullet go?
[10 pts.} What is the bullet's speed when it returns to its starting point?
(1)
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Ph~sics
221U
Fall 2012 - Nmcmbcr 2
Name:
;;
Exam 2
Vnid: - - - Discussion TA: Bryant
Justin
Will
Yuan
Da\ id Ailion
3
SHOW ALL WORK!! Place a circle or box around each answer. Specify units for each answer. Report aU numbers to two signifieant figures. A block of mass m = 0.20 kg is at rest at the height h = 4.0 m on a smooth inclined plane as shown. It slides down onto a
frictionless surface and collides inelastically with a second block of identical mass. The velocity ofthe fITSt block
immediately after the collision is I4 its velocity immediately before the collision and is in the same direction. The floor to
the right of the second block is rough with a coefficient of kinetic friction J4 = 0.50. As result, the second block slides a
distance d before coming to rest.
(a)
(b)
(c)
[5 pIS.} Calculate the speed V2 (in mls) ofthe second block immediately after the collision.
[J 0 pIs'] Calculate (in J) the energy lost in the collision.
[10 pIS.} Calculate (in m) the distance d that the second block travels before coming to rest.
a.) ~,.<v,1. =~h . ~ VI = /'2'!J~
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Physics 2210 Fall 2012 - November 2
David Ailion
." Name:
B(!JaYLi
Discussion T
~
Justin
Will
4
Exam 2
Unid: _ _ _---::=,--_ _ _ _ _ _ __
Yuan
SHOW ALL WORK!! c
Place a circle or box arQund each answer. Specify units for each answer. Report all numbers to two significant figures. A child's pogo stick stores energy in a spring with a force constant of
2.55 x 104 N/m. At position A (XA = - 0.120 m), the spring compression is a
maximum and the child is momentarily at rest. At position B (XB = 0), the
spring is relaxed and the child is moving upward. At position C, the child is
again momentarily at rest at the top of the jump. The combined mass of the
child and the pogo stick is 25.5 kg.
(a) (b) (c) (d) a)
B
A
[5 pts.} Calculate the total energy of the child~stick-Earth system if
both gravitational and elastic potential energies are zero for x = o.
[5 pts.} Determine Xc.
[8 piS.} Determine the value of x for which the kinetic energy of the
system is a maximum.
[7 piS.} Calculate the child's maximum upward speed.
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