PHYS 112

 

Mechanics
FALL 2006

 

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Online Physics

Java Applets of Interest

Vector Addition/Subtraction

Free body Diagram

Physic Formula Sheet

Problem Sets

Problem Set 6 – Due October 31 @ 3pm

Take online quiz!

Conceptual question 16 from text.  Must be typed.  Double spaced <= 1 page.

Problem 19, Problem 30, Problem 40, Problem 49

 

Problem Set 5 – Due Oct 20 @ 4pm

Take your question 48 from Chapter 4 from last weeks assignment and write a well formed (short!) report on exactly how you used Newton’s 3 laws to solve the problem.  I am not interested in the math, just the application of the 3 laws.

One definition of a conservative force is: A force is conservative if the net work done by the force in moving an object around a closed loop is zero.  Hypothesis:  Gravity is a conservative force.  Test your hypothesis by calculating the net work (i.e. add up all the work done on each segment) done by gravity in the following closed loop:  Start at 0.0m, 0.0m.  5.0-kg box moved right to (2.0m, 0.0m), object is then moved upwards to (2.0m, 3.0m); object is moved left to (0m,3m); finally object is moved downwards to (0.0m, 0.0m). Note: only calculate the work done by gravity!  Finally make a conclusion regarding your hypothesis.

Solve question 48 from Chapter 4 using Work-Energy – if possible!

Do questions on WebCT (should be easier this week!)

Problem Set 4 – Due Oct 13 @ 4pm

Complete questions on WebCT .  You can attempt 5 times!  See me for login problems.

A 900-kg car is involved in an accident.  The car was originally going at 100km/h when the driver saw a moose on the road.  The driver (75-kg) slammed on the brakes, resulting in a deceleration of 0.9g.  What is the net force on the car?  How far will it take the driver to stop?  How much time to stop?  If the driver hits the moose 2.0s after applying the brakes, how fast is the car going when it hits the moose.  Suppose the car is moving this fast when it hits the moose.  If we treat the moose as a barrier causing the rest of the car to stop over a distance of the crumple zone of the car (approximately 40cm), what force does the moose exert on the car?  What force is exerted on the driver of the car?  Given serious injury will occur if the average acceleration on the driver exceeds 20g, do you expect the driver to be injured when striking the moose?

Do question 48 in Chapter 4.

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Problem Set 3 – Due Sept 28 @ 2 pm

Complete questions on WebCT .  You can attempt 5 times!  See me for login problems.

Chinook salmon are able to move upstream faster by jumping out of the water periodically;  this behaviour is called porpoising.  Suppose a salmon swimming in still water jumps out of the water with a speed of 6.26m/s at an angle of 45 degrees, sails through the air a distance L before returning to the water, and then swims a distance L underwater at a speed of 3.58m/s before beginning another porpoising maneuver.  Determine the average speed of the fish.

S student stands at the edge of a cliff and throws a stone horizontally over the edge with a speed of 18.0m/s.  The cliff is 50.0m above a flat, horizontal beach.  How long after being released does the stone strike the beach below the cliff?  With what speed and angle of impact does the stone land?

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Problem Set 2 – Due Sept 22 @ 4pm

Chp2 Conceptual #12, Problems 22, 37, 46, 61 (Provide graphical solution of question 61). Also hand in the inspectors report for your boss Hugo on the Maria Andretti case First Day on the Job.

22. The velocity vs time graph for an object moving along a straight path is shown below.  Find the average acceleration of the object for time intervals: 0-5s, 5s-15s, 0-20s. (b) find the instantaneous acceleration at 2.0s, 10s and 18s.

37. A car starts from rest and travels for 5.0s with a uniform acceleration of +1.5-m/s2.  The driver then applies the brakes, causing a uniform acceleration of -2.0m/s2.  If the brakes are applied for 3.0s, (a) how fast is the car going at the end of the braking period, and (b) how far has the car gone?

46. Traumatic brain injury such as a concussion results when the head undergoes a very large acceleration.  Generally, an acceleration less than 800m/s2 lasting for any length of time will not cause injury, whereas an acceleration greater than 1000m/s2 lasting for ate least 1ms will cause injury.  Suppose a small child rolls off a bed that is 0.40 m above the floor.  If the floor is hardwood, the child’s head is brought to rest in approximately 2.0mm.  If the floor is carpeted, this stopping distance is increased to about 1.0cm.  Calculate the magnitude and duration of the deceleration in both cases, to determine the risk of injury.  Assume that the child remains horizontal during the fall to the floor.  Note that a more complicated fall could result in a head velocity greater or less than the speed you calculate.

61.  A young woman named Kathy Kool buys a sports car that can accelerate at the rate of 4.90m/s2.  She decides to test the car by drag racing with another speedster, Stan Speedy.  Both start from rest, but experienced Stan starts 1 second before and moves with a constant acceleration of 3.50m/s2, find the (a) time it takes Kathy to overtake Stan, (b) the distance she travels before she catches him, and (c) the speeds of both cars at the instant she overtakes him.

 

 

Problem Set 1 – Due Sept 14 (1pm).  Chp 1

Conceptual #1: Estimate the order of magnitude of the length, in meters, of each of the following: a) mouse b)pool cue c) basketball court d)elephant e) city block

#2 What types of natural phenomena could serve as time standards?

Problem 32:  Grass grows densely everywhere on a quarter-acre plot of land.  What is the order of magnitude of the number of blades of grass?  (1 acre = 43560 ft2)

Problem 39: For the right angle triangle a=6.00m, b=? c=9.00m below what are a) the length of the unknown side b) tangent of A and c) the sine of B.  Note side a is opposite angle A and side c is the hypotenuse and is opposite the right angle.

Provide 2 examples where you would use unit conversions in your everyday life.

According to ICBC: 679 car crashes per day means that there is a car crash every 3 minutes.  Confirm this assertion.

 

Lecture Schedule

 

Week 
Starting

Topic

Chapter

Concepts/ PBL

Sept 4

Course Overview

n/a

 

 

Units, Math Review

n/a

 

Sept 11

Graphing/Kinematics (1-D)

2

Speed Trap

 

 Sept 18

Vertical Motion (2.6)

Motion in 2-D (Projectile)

2.6, 3.1-3.4

 

Sept 25

Forces – Newton’s laws

4 (all)

 

Oct 2

Forces Newton’s Laws

4 (all)

 

Oct 9

Energy

 

5(all)

Key Concept:

Mechanical energy may be conserved

Friction removes Mechanical energy from the system

Oct 16

Energy

5(all)

 

 Oct 23

Cons of Momentum

6

 

Oct 30

Rotational Kinematics

7.1-7.3

 

Nov 6

Gravitation/

7.4-7.6

 

Nov 13

Rotational Dynamics

8.1, 8.2, 8.3, 8.4

 

 Nov 20

Solids and Fluids

9