n exam 02: chapters 14 and 15 - uca · formulae or solutions to any other problems. • express...

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Exam 02: Chapters 14 and 15Instructions

• Solve each of the following problems to the best of your ability. You have two hours in which to complete this exam.

• You may use your calculator and your textbook.

• Read and follow the directions carefully. Pay attention to the hints!! They are there for a reason!!

• Solve using the method required by the problem statement. If you are not explicitly required to use a specific technique, please be sure to show sufficient work so that your method is obvious.

• Show all your work. Work as neatly as you can. If you need scratch paper, blank sheets will be provided for you.

• It is permissible to use your calculator to solve a system of equations directly. If you do, state this explicitly. f you need to use a solver to evaluate a trig equation, you will be allowed to either use your mobile device briefly, or you may borrow mine. You may only use the device to solve the specific equation; you may not look up formulae or solutions to any other problems.

• Express your answer as directed by the problem statement, using three significant digits. Include the appropriate units.

ScoringProblem 01: Chapter 14 /15

Problem 02: Chapter 14 /15





ENGR 3311: ENGINEERING DYNAMICS! SPRING 2017

EXAM 02! PAGE 1/7

Problem 01 Chapter 14: Problem R14–3

The small 2-lb collar starting from rest at A slides down along the smooth rod. During the motion, the collar is acted upon by a force F = (10i + 6yj + 2zk)lb,where x, y, z are in feet. Determine the collar’s speed when it strikes the wall at B.

Hint: If the force has x, y, z components and the displacement also has x, y, z components, then you have to make sure you account for all of the work done. Notice that only the x-component is constant. And don’t forget about gravity, either.


EXAM 02! PAGE 2/7

Problem 02 Chapter 14: Problem 14–74

The assembly consists of two blocks A and B which have masses mA = 20 kg and mB = 30 kg. Determine the speed of each block when B descends yB = 1.5 m. The blocks are released from rest. Neglect the mass of the pulleys and cords.

Hint: Start with the dependent motion to get the relationships between yA and yB, then vA and vB.


EXAM 02! PAGE 3/7


The pan of negligible mass is attached to two identical springs with stiffness k = 250N/m. If a box with m = 10-kg is dropped from a height of 0.5 m above the pan, determine the maximum vertical displacement d. Initially each spring has a tension of 50 N.

Hint: Skip the impact and just conserve total energy. Which means you need to include the spring potential before the box every hits the pan. Which means you need the unstretched length lo of the spring, and the ∆l of the spring at both positions.


EXAM 02! PAGE 4/7

Problem 04 Chapter 15: Problem R15–11

A block with m = 20-kg is originally at rest on a horizontal surface for which the coefficient of static friction is µs = 0.6 and the coefficient of kinetic friction is µk = 0.5. If a horizontal force F is applied such that it varies with time as shown, determine the speed of the block at t = 10 s.

Hint: First determine the time needed to overcome friction and start the block moving.


EXAM 02! PAGE 5/7


Two smooth disks A and B have the initial velocities shown just before they collide. If they have masses mA = 4 kg and mB = 2 kg, determine their speeds just after impact. The coefficient of restitution is e = 0.8.

Hint: Align your coordinate system with the line of impact. I would make the initial direction of vB the +y direction, but that’s just me.


EXAM 02! PAGE 6/7


A 4-lb ball B is traveling around in a circle of radius r1 = 3 ft with a speed (vB)1 = 6ft/s.If the attached cord is pulled down through the hole with a constant speed vr = 2 ft/s, determine the ball’s speed at the instant r2 = 2 ft. How much work has to be done to pull down the cord? Neglect friction and the size of the ball.

Hint: Conserve angular momentum, then work-energy to find work done by cord on ball.


EXAM 02! PAGE 7/7

n exam 02: chapters 14 and 15 - uca · formulae or solutions to any other problems. • express...

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