Physics 121 Midterm 2.
November 1, 2010
Exam form 0
1
This is a closed book exam. Use your own formula sheet, 8½ x 11 inches, double sided,
handwritten.
You may only use your own calculator; NO SHARING.
ANY
manipulation of electronic equipment (I-Pod, cell phone, laptop computer, pager, etc.)
other than your calculator is strictly prohibited, and will result in a zero on this exam.
Answer all problems on the bubble scan sheet.
Before you start,
enter your name and student ID number on the
answer sheet
.
This is exam form 0.
Mark 0 on the first digit of
birth day on the bubble scan sheet
.
(Do not fill in your birth date.)
There are twenty questions, each of which carries equal weight.
Question 1: (1 point)
A ski lift moves 3000 people up a1000 m mountain in one hour.
Assuming the mass of a
typical skier is 50 kg, how much power is required to run the ski lift?
P = W/
∆
t = F*d/
∆
t = mgh/
∆
t =
(number of people)(mass/person)*g*h/
∆
t
= (3000)(50 kg)(9.81 m/s2)(1000m)/(3600s) = 409 kW
Question 2: (1 point)
Note: The work done by gravity is negative,
–
mgsin
Θ
d, because gravity is working
opposite the motion and tries to take energy away from the block, not add to it.
Energy
is not conserved because the speed is constant, so the person is adding energy to
overcome gravity.
A person pushes a block of mass m up a frictionless plane
at a constant speed, exerting a force F
push
.
Which of the
following statements is correct?
The work done by F
push
is W
push
= mg*sin
Θ
*d

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