Practice Exam 1 ANSWERS

1.         c

2.        

3.        

            What you had to know: 

            a) Vertical and horizontal motions are independent.  So horizontal motion can be

ignored.

b) When the shell reaches the top of its trajectory, its vertical velocity goes to

zero.  So the problem is the same as dropping a the shell from 1 mile up and

asking what the final velocity is (i.e. upward motion is time reverse of

downward motion).

c)  You can ignore air resistance for a rough answer.

d)  The formula of the magnitude of the velocity v of an object dropped from

height x is (question 5 of Quiz 1).

e)  They way to convert 1 mile (= 5280 ft) into meters. [Could also have used 1

mile = 1.61 km = 1610 m]

4.         True.   (From Lab #1)

5.         True.   (From Lab #1)  Air resistance at low speed is proportional to v, and at high

speed to v².

6.         True.  [It has a magnitude and a direction.]

7.        

            So answer = 100 m/s north, 0 m/s east.

8.         100 mph north, 0 mph east

            What you had to know:

            a) The plane’s velocity relative to the ground is the sum of the plane’s velocity

relative to the air and the air’s velocity relative to the ground. (Common sense).

            b) You can choose a simple coordinate system:  +x direction = North,

    +y  direction = East.

c) Motion South is the negative of motion North, i.e. motion in the –x direction.

    Motion West is the negative of motion East, i.e. motion in the –y direction.

d) How to write down vectors given their components.

e) How to add vectors.  (See question 7)

9.         speed =

10.      

            What you had to know:

            a) Formula for acceleration of object moving in circle at constant speed.

            b) Definition of speed as distance/time.

            c) A minute hand takes 1 hour to rotate once.

11.      

            What you had to know:

            a) 1 rotation = 2π radians

            b) 1 rotation take 24 hours.

            c) 1 hour = 3600 seconds.

            d) angular velocity = angle/ time

12.        (where 1 newton = 1 kg m/s²)

            What you had to know: Newton’s 2^nd Law.

13.       True.

14.       False.

15.      

            What you had to know:  Trig.  Or notes from lecture.

16.      

            What you had to know:  The definition of tension.

17.       1^st.

18.       Yes.  (definition of equilibrium given in lecture)

19.       300 lbs upward.  [The woman is not moving. So she is in equilibrium.  So forces

on her must cancel.]

20.       No.  [Particle is changing its direction, therefore its velocity. See Quiz #1]

21. 18.9 rpm