Download Physics Department Physics 101 - Physics Department ,Kuwait

Physics Department
Physics 101
Spring Semester
Second Midterm Exam
Saturday, April 9, 2016
3:00 – 5:00 p.m.
Student’s Name: ………………..………………….…………………………………….…………
Student’s Number: ….……………………………………
Section: ……………………
Choose your Instructor’s Name:
Prof. Fikry El-Akkad
Prof. Yacoub Makdisi
Dr. Hasan Raafat
Dr. Ahmed Al-Jassar
Dr. Fatema Al Dosari
Grades:
#
Dr. Abdul Khaleq
Dr. Abdul Mohsen
Dr. Belal Salameh
Dr. Tareq Al Refai
Dr. Nasser Demir
For Instructors use only
Q1
Q2
Q3
Q4
Q5
SP1
SP2
SP3
SP4
SP5
SP6
SP7
SP8
SP9
SP10
SP11
LP1
LP2
Total
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
20
Pts
Important:
1.
2.
Answer all questions and problems.
Full mark = 20 points as arranged in the above table.
i. 5 Questions
ii. 11 Short Problems
iii. 2 Long Problems.
3. No solution = no points.
4. Use SI units.
5. Check the correct answer for each question.
6. Assume g = 10 m/s2.
7. Mobiles are strictly prohibited during the exam.
8. Programmable calculators, which can store equations, are not allowed.
9. Please write down your final answer in the box shown in each problem.
10. Cheating incidents will be processed according to the university rules.
GOOD LUCK
Kuwait University – Science College – Physics dept. – PHYS 101
Spring 2015/2016 (April 9, 2016)
Part I: Questions (Choose the correct answer, one mark each)
Q1. A book stands at rest on a table with a horizontal surface. The reaction force to the book’s
weight is
a. the gravitational force exerted by the book on the Earth.
Third Law of Newton
b. the gravitational force exerted by the table on the book.
c. the normal force exerted by the Earth on the book.
d. the normal force exerted by the table on the book.
e. the normal force exerted by the book on the table.
Q2. One observer drops a ball from the top of a building while another observer at the bottom of the
building observes its motion. On which of the following will the two observers disagree?
(Neglect air resistance)
a. the change in the ball’s potential energy.
b. the ball’s kinetic energy at some point during its motion. Zero level of potential energy is
arbitrary but ΔUor ΔE are not
c. the change in the ball’s total mechanical energy.
d. the magnitude of the ball’s acceleration.
e. the ball’s potential energy as measured relative to each observer’s position.
Q3. A boy of mass m rides on a Ferris wheel of radius R moving at constant speed v as shown in the
figure. At the lowest point in the trajectory, the boy’s apparent weight is
a. less than mg.
R
b. greater than mg.
c. equal to mg.
d. equal to
.
e. equal to mv2/R.
Q4. The kinetic energy of an object depends upon
a. the relative distance between the object and another object.
b. the frame of reference in which the motion is measured.
c. the mass and the acceleration.
V depends on frame of reference
d. only on the speed.
e. the mass and the velocity.
Q5. A normal force
n a. can only do positive work
Work = 0
b. can only do negative work
c. can do either positive, negative, or zero work.
d. can do work only in the opposite direction of friction
e. can never do work
n
Positive work
Negative work
1 Kuwait University – Science College – Physics dept. – PHYS 101
Spring 2015/2016 (April 9, 2016)
Part II: Short Problems (1 mark each)
SP1. Vectors
and
Calculate the scalar product
.
30 and
, with magnitudes
∙
40, respectively, are shown in the figure.
.
Y
30 40 cos 60
10 ̊
600
X
20 ̊
600
Answer :
SP2. A 2.4 kg object is initially at rest. Find the net work (in J) done on the object if its velocity
changes to 8.00 ̂
Σ
4.00 ̂ m/s.
&
8
2.4 80 Σ
4
80
96
96
Answer:
SP3. A car rounds a flat (unbanked) curve on a highway. The coefficient of static friction between the
tires and the road is µS=0.40. If the car is to round the curve at 12 m/s, find the minimum radius R
(in m) of this flat curve in order to avoid skidding.
⟹
⟹ R
⟹
.
36
Answer:
36
2 Kuwait University – Science College – Physics dept. – PHYS 101
Spring 2015/2016 (April 9, 2016)
SP4. A block m1 is placed on the top of another block m2 as shown in the figure. A horizontal force F is
applied to the block m2, and the block m1 is tied to the wall. Assuming all surfaces are rough,
draw a free-body diagram for the block m2.
m1
FN
m2
fk1
F
fk2
F21 (m1g)
m2g
Answer
SP5. A block of mass m=2 kg is placed on a frictionless horizontal surface and is attached to a spring
with force constant k=800 N/m. The block is pulled 6 cm to the right of equilibrium and is released
from rest. Find the speed (in m/s) of the block as it passes through the equilibrium position.
0
0
0.06
1.2 /
1.2
Answer:
/
SP6. A block of mass 4.0 kg is suspended from a system of three light cables, A, B, and C and is kept at
equilibrium, as shown. Find the tension (in N) in cable A.
53 ̊
Σ
2
0
sin
Σ
TA sin θ
0
TB sin θ
.
A
B
C
TA cos θ
53 ̊
TB cos θ
25
m
mg
Answer:
25
3 Kuwait University – Science College – Physics dept. – PHYS 101
Spring 2015/2016 (April 9, 2016)
SP7. A 3730 kg elevator loaded with passengers is moving up at a constant speed of 2 m/s. What is the
power output (in hp) of the motor? (1 hp=746 watts)
.
F
, constantspeed
3730 10 2
74600
100
mg
100
Answer:
SP8. An applied constant force of magnitude F = 48 N parallel to a rough inclined surface, pushes a block
of mass m = 4.0 kg up the inclined surface. If the block accelerates at a rate of 2 m/s2, find the
coefficient of kinetic friction (µK) between the block and the surface.
m
n
sin
F
36.9°
cos
mg cos θ
mg sin θ
fk
0.5
0.5
Answer:
SP9. A bead of mass 2 kg slides without friction around a loop-the-loop. The bead is released from rest
at a height h = 4R, where R = 8 m is the radius of the loop-the-loop. Find the normal force (in N)
exerted on the bead from the surface at point A.
n
0
4
smooth
2
2
2 10 16
2
mg
A
h
320
8m
20 = 60 N
Answer:
60 N
SP10. A ball of mass m = 4 kg, attached to a thin rope of length L = 2 m, rotates in a vertical circle, as
shown in the figure. Find the tension (in N) in the rope when the ball reaches point A, where its
speed at point A is 5 m/s. cos
4
50
4 10 cos 120
20
m
A
or
cos 60
cos 60
mg sin 60
mg cos 60
L
60 ̊ T
30 ̊
mg
120 ̊
30
Answer:
30
4 Kuwait University – Science College – Physics dept. – PHYS 101
Spring 2015/2016 (April 9, 2016)
SP11. A horizontal applied force of magnitude F=120 N is applied to a system of blocks which move
together to the right on a frictionless horizontal table, as shown in the figure. If the three blocks do
not slip with respect to each other, and the coefficients of friction between all blocks are the same,
(µK=0.4 and µS=0.7), find the magnitude of the friction force (in N) between m2 and m3.
⟹ 3 /
0.7 150
rough surface
105
15 3
m1 = 5kg
m1
m2 = 10kg
m3 = 25kg
m2
smooth surface
45
m3
45
Answer:
Part III: Long Problems (2 marks each)
LP1. A 2 kg object moving at 6 m/s on a rough horizontal surface comes to a complete stop after
traveling a distance of 4 m. Assume the frictional force is constant.
a. Use the work-energy theorem to calculate the magnitude of the frictional force (in N)
stopping the object.
Σ
0
9
b. What is the magnitude of the acceleration (in m/s2) of the object?
⟹ 4.5 /
c. Find the coefficient of the kinetic friction between the block and the surface.
μ ⟹μ
0.45
Answer:
9
Answer:
4.5
Answer:
0.45
/
5 Kuwait University – Science College – Physics dept. – PHYS 101
Spring 2015/2016 (April 9, 2016)
LP2. Two blocks of mass m1 = 20 kg and a block of mass m2 = 4 kg are attached to a light rope passing
over a massless, frictionless pulley as shown in the figure. Block m1 lies on a rough incline of angle
= 36.9 ̊ and coefficient of kinetic friction µK = 0.2. The system of block is released from rest and
moves as shown. Find
a. the magnitude of the acceleration (in m/s2) of the two objects.
T
m1
m2
θ
sin
μ cos
sin
(1)
(2)
T
m
fk
cos
2 /
m1g sin θ
m1g cos θ
a. the tension (in N) in the cord.
4 10
2
48
Answer:
2 /
Answer:
48
6 m2g