Course: PHYS 204-Sections EC & EC2
Date: December 09/2020
Exam time: 14:00 – 16:00
Instructor: Seyyed Nima Nateghi
Multiple Choice
1. (2 marks) In a mass-spring system, a block oscillates with simple harmonic motion along
the x axis. Its displacement varies with time according to the equation 𝑥 = 5 cos(𝜋𝑡).
The magnitude of the acceleration of the body at t = 1 second is approximately:
a) 3.5 m/s2
b) 49 m/s2
c) 14 m/s2
d) 43 m/s2
e) 4.3 m/s2
2. (2 marks) A cylinder with mass 𝑚, length 𝐿, and radius 𝑅 is placed next to a disk with
mass 𝑚 and radius 𝑅 on an incline surface. If we let them roll down, which one will have
a higher speed at the bottom of the incline surface? Ignore the effect of resistive forces.
Assume that the cylinder and the disk roll without sliding. We have (𝐼 𝐶𝑀 )𝐷𝑖𝑠𝑘 =
1
(𝐼𝐶𝑀 )𝐶𝑦𝑙𝑖𝑛𝑑𝑒𝑟 = 𝑚𝑅2 .
2
a) Cylinder
b) Disk
c) They will have the same speed
d) Cannot be determined
3. (2 marks) In car accidents, how do airbags save passenger’s life?
a) They decrease the change in momentum of the passenger, compared to a car with no
air bag
b) They increase the interaction time during which the passenger is brought to rest and
hence decrease the force applied on the passenger
c) Airbags do not affect the force applied on the passenger, they only allow more time
for the body to adapt to this force.
1
, 4. (2 marks) In a figure skating tournament, Alice is spinning with her
arms fully stretched. Suddenly, a bird sits on her hand. What happens
to her angular speed?
a) It increases
b) It decreases
c) It remains constant
5. (2 marks) If a tennis ball and a bowling ball have the same momentum, which one has a
larger kinetic energy?
a) The bowling ball
b) The tennis ball
c) They have the same kinetic energy
6. (2 marks) In a mass-spring system in simple harmonic motion, a block moves back and
forth along the x-axis from 𝑥 = – 𝐴 to 𝑥 = +𝐴 with period 𝑇. If at time 𝑡 = 0 it is at 𝑥 =
3
0 and is moving in +𝑥 direction, which one is true at 𝑡 = 4 𝑇?
a) it is at 𝑥 = 0 and is traveling toward 𝑥 = +𝐴
b) it is at 𝑥 = 0 and is traveling toward 𝑥 = −𝐴
c) it is at 𝑥 = +𝐴 and is at rest
d) it is at 𝑥 = −𝐴 and is at rest
e) it is between 𝑥 = 0 and 𝑥 = −𝐴 and is traveling toward 𝑥 = −𝐴
7. (2 marks) A 5-kg mass is suspended by a string from the ceiling of an elevator that is
moving upward with a speed which is decreasing at a constant rate of 2 m/s in each
𝑚
second. What is the tension in the string supporting the mass? Take 𝑔 = 10 𝑠 2.
a) 50 N
b) 40 N
c) 60 N
d) 10 N
e) 45 N
8. (2 marks) A ball of mass 𝑚 is released from rest from a
height of 7 𝑚 on a frictionless inclined surface. Calculate
the velocity of its center of mass if it rolls down the
inclined surface without slipping (Although the surface is
𝑚
frictionless, assume that the ball rolls). Take 𝑔 = 10 𝑠 2.
2
𝐼𝐶𝑀 = 5 𝑚𝑅2 .
𝑚
a) 10 𝑠
2
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