University
Physics Kuwait Department
Final Examination
Physics 101 June 16, 2009 8:00-10:00 am
Name: Student No. ... ___________________________________________________________________________ Instructors Name:
# Q1 Q2 Q3 Q4 P1 P2 P3 P4 P5 P6 P7 P8 Points
Total
Important 1. Answer all questions and problems. 2. Each question will be assigned 1 point. 3. Each problem will be assigned 2 points 4. No solution = no points 5. Mobiles and pagers are not allowed during the exam 6. Programmable calculators are not allowed. Good Luck
Part I : MC Questions 1. A bomb at rest explodes into two fragments of un-equal masses that go in opposite directions. What is the total momentum of the system after the explosion? a) b) c) d) 0 50 kg.m/s -25 kg.m/s There is no enough information.
2. The elastic potential energy in a spring is a) b) c) d) Always positive Always negative Sometimes positive and sometimes negative None of the above
3. A projectile is thrown with an initial velocity point in its path, its speed (in m/s) will be a) b) c) d) zero 6 8 10
m/s. When it reaches the highest
4. A chain of three identical links is lifted upward with constant speed by an applied force F as shown. The net force on link 3 is a) zero b) F c) d)
Part II : Problems
1. An object is moved a distance 2 m in the positive x-direction. One of the forces acting on the object is F = 2 i + 3 j (in N). Find the work done (in Joule) by this force.
2. A car starts to move from rest along a straight line and accelerates at a rate of 1.6 m/s2 for 20 seconds. Then it continues moving with a constant speed for 70 seconds. Find the total distance (in m) covered by the car.
Finding x1
Finding v
Finding x2
Finding x x = x1 + x2 = 320 + 2240 = 2560 m
3. In Disneyland a large cylinder of radius 4.0 m spins about a vertical axis. When it reaches an angular speed , the cylinder floor drops down and the passengers inside it are held up against the wall (see the figure). If the coefficient of static friction between the passenger and the wall is 0.10, find the minimum of value .(in rad/s).
=
= 20 m/s
4. A block m1 = 2.0 kg is placed on top of another block m2= 5.0 kg and the system moves on a rough horizontal surface (k= 0.20 ) under the action of a force F = 30 N applied to m2. Find the minimum coefficient of static friction between the two blocks such that m1 does not slide off.
=
a = 2.28 m/s2
5. A 10-kg block is released from point A on a track ABCD as shown in the figure. The track is frictionless except for the portion BC, of length 6 m. The block travels down the track and hits a spring of force constant k=2000 N/m and compresses it a distance of 0.30 m from its equilibrium position before coming momentarily to rest. Determine the coefficient of kinetic friction between the block and the portion BC of the track.
Wf = E = Ef - Ei Wf = (Ufg + Ufs + Kf ) (Uig + Uis + Ki ) -k m g d = ( 0 + k x2 + 0 ) ( m g h + 0 + 0 ) -k (10) (10) (6) = (2000) (0.3)2 10(10)(3)
k = 0.35
6. A billiard ball A moving at 5 m/s strikes a stationary ball B of the same mass. After the collision ball A moves at 4 m/s at an angle of 37 with respect to the original line of motion. Assuming an elastic collision, find the magnitude of the final velocity (in m/s) of ball B.
mvAi = mvAf cos(37) + mvBf cos(53) 5 = 4 cos(37) + vBf cos(53) vBf = 3 m/s Another Solution = =
7-A particle of mass m = 0.50 kg is attached to the surface of a hoop of mass M = 2.0 kg and radius R = 0.40 m (see figure). If the system starts from rest at t=0 and rotates about the z axis with angular acceleration = 2.0 rad/s2, find its kinetic energy (in joule) at t= 60 s (Ihoop = MR2).
= 0 + t = 0 + 2 (60) = 120 rad /s K = I 2 = ( MR2 + mR2 ) 2 K = ( 2 + 0.5 ) (0.4)2 (120)2 K = 2880 J
8- A force F = - 2 k ( in Newtons) is applied to an object that is pivoted about a fixed axis though point O along the z-direction (see figure). If the force is applied at a point of coordinates ( 2, 4, 0 ) ( in meters), find the magnitude of the net torque (in mN) and the angle it makes with the positive z axis.
Angle with z axis = 90 degree