AP Physics: Friday SEP 3:

Key Concept's) Today: Ch 1 & 2 Review, Go over Free Response Q's from Summer H/W

True or False (if False, Why)

1. If an object is moving, something has to be pushing it.

2. If you apply a constant force to an object, it will move with constant velocity.

3. If  no force acts on it, a moving object will eventually stop.

4. Inertia is a force.

5. A 1,000 kg object in space would require less net force to accelerate it  from rest to 25 m/s than an object on Earth because it doesn't have to overcome either gravity or friction.

6. A force is a vector quantity; there is always a direction associated with it.

7. If an object is moving to the right and slowing down, then the net force on the object is directed towards the left.

8. The direction of net force on an object is ALWAYS the same direction of acceleration.

1. False,1st Law

2. False, not if the force is a net force (2nd law)

3. False, not in space (no friction - 1st law)

4. False, its related (property of) directly to matter

5. False, requires same net force (2nd law)

6. True

7. True

8. True

Chapter 1 & 2:

1. The sum of three vectors given in components as A_x = 3, A_y = 4, B_x = 3, B_y = -3, C_x = -6, C_y = -2

Find:

a. R_x =      b. R_y =        c. Resulting vector (polar)

2. A vector 6.0  ∟60⁰,     Find:

            A_x =                 A_y =

For the next several questions, consider the velocity-time plot below for the motion of an object along a horizontal surface. The motion is divided into several time intervals, each labeled with a letter.

3. During which time interval's or points, if any, are there no net forces acting upon the object? List all that apply.

4.  During which time interval's or points, if any, is the acceleration negative? List all that apply.

i5. During which time interval's, if any, is the net force acting upon the object directed toward the left? List all that apply.

answers:

                        1. R_x = 0, R_y = -1,  1L270⁰

                        2. y = sin 60(6) = 5.2

                           x = cos 60(6) = 3

3.  B, D, F, H

4. C, G & points J, L

5. C, G & points J, L 

6. Estimation (no calculator): Use one sig fig and answer is one sig fig

(1.5 x 10⁴)(8.39 x 10¹³)   =  2 x 10¹⁸

7. Conversion:

• Work Coefficient
• Work Exponents
  • (multiply = add exponents)
  • (divide    =  subtract exponents)
• Cross out Labels

 10⁹  cm/sec   = ____ km/hr

    (4.20 x 10² km/hr) (100,000 cm) (1.00 hr)               

                                                (1.00 km)    (3600sec)

            à 11,666.6 or 11,700 cm/sec 

Notes:

a.    What is a ratio?

b.   What does proportional relationships mean?

 Direct:  y goes up, x goes up  (y = k x)

 Inverse: y goes up, x goes down  (y = k/x)  or   y = k (1/x²)

Examples

·             If an object travels at a constant speed, then the distance traveled is proportional to the time spent traveling.

·             The circumference of a circle is proportional to its diameter, with the constant of proportionality equal to π.

·             The amount of force acting on a certain object from the gravity of the Earth is proportional to the object's mass.

Worksheet for Tues