Your Name: _______________________ PHY203

Exam #1

Chapters 1-3

Fri., 2/19/10

Lecture Time: 1p.m.

1-10 _________________ (out of 60)

11 _________________ (out of 40)

Total _______________

Multiple choice answer sheet-shade in correct answers below

(one choice per problem):

	1	2	3	4	5	6	7	8	9	10
a
b
c
d
e

PHY203

Exam #1

Crib Sheet

Chapters 1-3

speed_AV = (total distance traveled)/Dt

Dr = r₂ – r₁ (displacement)

v_AV = Dr/Dt

a_AV = Dv/Dt

v_Inst = dr/dt

a_Inst = dv/dt

For constant acceleration:

x_f = x_o + v_ot + (1/2)at2

v_f = v_o + at

V_f2 = v_o2 + 2a(x_f - x_o)

use g = 9.81 m/s2, the acceleration due to gravity, unless otherwise directed

For a vector A with magnitude A and direction q (measured counterclockwise with respect to the x-axis):

A_x = Acos(q)

A_y = Asin(q)

A = (A_x² + A_y²)^1/2

tan(q) = A_y/A_x

quadratic eq. sol.: If ax² + bx + c = 0; then x = -b+(b²-4ac)^1/2/(2a)

1. The speed of sound in air is 343m/s. Find the speed in miles per hour of a supersonic plane flying at 10 times the speed of sound.

a. 0.59 mph

b. 128 mph

c. 331 mph

d. 7670 mph

e. 19,900 mph.

For problems 2 and 3, an object is moving along the x axis. At t=6.0 s, the object is at x=4.0m and its velocity is +4.5m/s. At t=10s, the object is at 11.0m and its velocity is -1.5m/s.

2. Find the average velocity of the object during the time interval 6-10 s.

a. 0.45 m/s

b. 0.75 m/s

c. 1.5 m/s

d. 1.75 m/s

e. 3.75 m/s.

3. Find the average acceleration of the object during the time interval 6-10 s.

a. -1.5 m/s²

b. -0.75 m/s²

c. 0.75 m/s²

d. 1.5 m/s²

e. None of the above

4. Determine the x and y components of a 30m/s velocity vector which makes an angle of 30⁰ counterclockwise from the positive x axis.

a. v_x= 15m/s, v_y= -26m/s

b. v_x= 26m/s, v_y= -15m/s

c. v_x= +15m/s, v_y= +26m/s

d. v_x= 26m/s, v_y= +15m/s

e. None of the above

5. Determine the x and y components of a 30m/s velocity vector which makes an angle of 60⁰ clockwise from the negative x axis.

a. v_x= -26m/s, v_y= -15m/s

b. v_x= -26m/s, v_y= +15m/s

c. v_x= +15m/s, v_y= -26m/s

d. v_x= -15m/s, v_y= +26m/s

e. v_x= +26m/s, v_y= -15m/s

6. Let A = -4i + 6j, B = 3i - 10j, C = -3A + 3B

Write the vector, C, in vector notation:

a. -3i - 48j

b. -3i - -12j

c. 21i - 48j

d. 21i - 12j

e. None of the above

For problems 7-10, on Planet XXX, the acceleration due to gravity is exactly 10m/s². Rocks are dropped from the top of a cliff at a height of 500m.

7. Case1: a rock of mass 1.5kg is dropped. Find the time, t, at which the rock hits the bottom of the cliff.

a. 5.0 sec.

b. 7.1 sec.

c. 10.0 sec.

d. 100 sec.

e. None of the above

8. Case 2: a rock of mass 3.0kg is dropped from the top of the same cliff as above. Find the time, t, at which the rock hits the bottom of the cliff.

a. 5.0 sec.

b. 7.1 sec.

c. 10.0 sec.

d. 100 sec.

e. None of the above

9. Case 3: the 1.5kg rock is thrown straight down with an initial speed of 40 m/s. Find the time, t, at which the rock hits the bottom of the cliff.

a. 0.45 sec.

b. 6.8 sec.

c. 13.5 sec.

d. 14.8 sec.

e. 29.5 sec.

10. Case 4: identical rocks of mass 1.5kg: rock a is dropped from the cliff at t=0 sec.; rock b is thrown straight down at t=2 sec. with an initial speed of 40 m/s. Find the time, t, at which the rocks are side-by-side.

a. 1.0 sec.

b. 2.0 sec.

c. 3.0 sec.

d. 4.0 sec.

e. 5.0 sec.

11. A missile is shot from a cliff with height H = 400m and initial speed of 50m/s and an angle q = 55^o,as shown below. Use g =9.81 m/s². Show your work.

a. Write the initial velocity vector, v_i, in vector notation, using the coordinate

system above.

b. Calculate the time in sec. that it will take for the missile to reach its highest point.

c. Calculate the time in sec. that it will take for the missile to hit the ground.

d. Calculate the x position at which the missile will hit the ground.

e. Write the final velocity vector (just as striking the ground), v_i, in vector

notation, using the coordinate system above.