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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