Chapter 1 Quick Review - Department of Physics



TA: Tomoyuki Nakayama February 8th – February 9th, 2010

PHY 2048: Physics 1 with Calculus, Spring 2010

Review: Chapter 7.1-7.9

The purpose of this review is to refresh your memory. Physics is a cumulative subject, so make it sure that you understand basic concepts and typical problem solving techniques in previous chapters before moving on to a new chapter.

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A. Work & Kinetic Energy

1. How much work is done by a force F = (2 N)i + (3y2 N)j with y in meters, that moves a particle from a position ri = (2 m)i+(1 m)j to a position rf = -(4 m)i + (4 m)j.

2. A block is sent up a frictionless ramp along which an x axis extends upward. The figure on the right gives the kinetic energy of the block as a function of position x; the scale of the figure’s vertical axis is set by Ks = 100 J. If the initial speed of the block is 5.00 m/s, what is the normal force on the block?

B. Work Done by Gravitational Force & Spring Force

1. Write down the work done by the gravitational force and the work done by the spring force. Specify under what condition they do positive work on an object.

2. A block lies on a frictionless horizontal surface and attached to one end of a spring of k = 500 N/m. The other end of the spring is fixed. A horizontal force F = 40 N is applied to the block, stretching the spring until it stops. Find the position of the block when it stops and that when its speed is maximum.

3. A 0.2 kg block is dropped onto a relaxed vertical spring of spring constant k = 300 N/m. The block sticks to the spring and compress the spring 0.20 m before it momentarily stops. What is the speed of the block before it hits the spring?

C. Power

1. An initially stationary 2.00 kg object is accelerated by a single constant force to a speed of 10.0 m/s in 5.00 s. Find the average power due to the force over the 5 s interval and the instantaneous power at the end of the interval.

TA: Tomoyuki Nakayama February 8th – February 9th, 2010

PHY 2048: Physics 1 with Calculus, Spring 2010

Practice Exam Problems (Chapter 7.1-7.9)

Working on this problem set is optional, but it is strongly recommended. It is highly likely that some of these problems will appear in the exams. Do it on a weekly basis. Cramming is tiring and sometimes it ends up in a disaster.

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1. A man pushes an 80-N crate a distance of 5.0 m upward along a frictionless slope that makes an angle of 30º with the horizontal. His force is parallel to the slope. If the speed of the crate decreases at a rate 1.5 m/s2, then the work done by the man is (Work) a. -200 J b. 61 J c. 140 J d. 200 J e. 260 J

2. A 8000-N car is traveling at 12 m/s along a horizontal road when the brakes are applied. The car skids to a stop in 4.0 s. How much kinetic energy does the car lose in this time? (Kinetic Energy) a. 4.8×104 J　　b. 5.9×104 J c. 1.2×105 J d. 5.8×105 J e. 4.8×105 J　

3. An ideal spring, with a pointer attached to its end, hangs next to a scale. With a 100-N weight attached, the pointer indicates “40” on the scale as shown. Using a 200-N weight instead results in “60” on the scale. Using an unknown weight X instead results in “30” on the scale. The weight of X is: (Hooke’s Law) a. 10 N b. 20 N c. 30 N d. 40 N e. 50 N

4. An ideal spring is hung vertically form the ceiling. When a 2.0-kg mass hangs at rest from it, the spring is extended 6.0 cm from its relaxed length. A upward external force is now applied to the block to move it upward a distance of 16 cm. While the block is moving upward the work done by the spring is: (Work done by spring) a. -1.0 J b. -.52 J c. -0.26 J d. 0.52 J e. 1.0 J

5. A woman lifts a barbell 2.0 m in 5.0 s. If she lifts it the same distance in 10s, the work done by her is: (Work done by gravitational force) a. four times as great b. two times as great c. the same d. half as great e. one fourth as great

6. A particle moving along the x-axis is acted upon by a single force F = F0e-kx, where F0 and k are constants. The particle is released from rest at x = 0. It will attain a maximum kinetic energy of: (Work Done by Variable Forces) a. F0/ k b. F0/ ek c. F0 k d. (1/2)( F0 k) 2 e. kF0ek

7. An escalator is used to move 20 People (60 kg each) per minute from the first floor of a department store the second floor, 5m above. Neglecting friction, the power required is approximately: (Power) a. 100 W b. 200 W c. 1000 W c. 2000 W e. 60 000 W

Answers: 1-c 2-b 3-e 4-a 5-c 6-a 7-c

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