Conceptual Physics Chapter 2: Linear Motion

 

PART I Problems (50)

Solve these problems on your own paper. Solve each problem on its own page, do not put more than one problem on a page! You must use the Three-Column-Method to receive any credit for your work.

 

                  1.   What is the average velocity of a car that travels the 145 km to Dallas in 2.5 h?

 

                  2.   A car accelerates from zero to 27 m/s (which is 60 mph) in 6 s.

a) what is the rate of acceleration?

b) What distance did the car travel while doing this?

 

                  3.   A stone is dropped from a clig 75 m high. Ignoring air resistance calculate the following:

a) the time it takes the stone to hit the ground

b) how fast the stone is going the instant before the ground stops it.

 

PART II: Short Answer (70)

Answer the questions below on your own paper. Put each question on its own page, do not put more than one question on a page. Answer each question in ‘a’, ‘b’, ‘c’ bullet format.

 

                  4.   Consider the SI unit for acceleration.

a) What is the SI unit for acceleration? Write this unit with and without the square.

b) Why does time enter twice in the SI unit for acceleration?

 

                  5.   Consider acceleration:

a) What two things could you be doing when you are accelerating?

b) How is it possible to accelerate without changing speed?

c) Give an example of an object that accelerates without changing position.

 

                  6.   Consider motion graphs:

a) Draw a p-t graph of an object moving at a constant velocity.

b) Draw a v-t graph of an object undergoing uniform acceleration.

 

True/False

Indicate whether the statement is true or false.

 

                  7.   To calculate average speed you have to ignore the parts of the trip when you were not moving since average speed is calculated from total didtance and only time in motion.

 

                  8.   The slope of a line on a p-t graph tells you the displacement while the slope of the line on a v-t graph tells you average velocity.

 

                  9.   The SI unit for velocity as well as for speed is the ms, or the meter-second.

 

                  10. The rate at which the speed or direction of an object changes is that object’s acceleration.

 

                  11. A position-time graph of an object that is accelerating has a line with an infinite number of slopes.

 

                  12. The terms ‘velocity’ and ‘speed’ can be used interchangeably because both terms refer to a vector and can be fully described as a rate of change of position.

 

                  13. A ball is thrown straight up into the air, at the top of its trajectory its velocity is zero for just an instant, during that same insiant, however, its acceleration is still 9.8m/s2.

 

                  14. Acceleration means that something is either speeding up, slowing down or changing direction.

 

                  15. When a car rounds a corner at a constant speed its acceleration is zero because it is neither speeding up nor slowing down.

 

                  16. As a rock falls freely, ignoring air resistance, its velocity increases, the distance the rock covers each second increases and the acceleration of the rock increases.

 

PART V: Multiple Choice (30)

Identify the choice that best completes the statement or answers the question.Carefully place your answer choice on your scantron answer document.

 

                  17. When you look at the speedometer of a car you are seeing the ___

a.

average speed.

c.

average acceleration.

b.

instantaneous speed.

d.

instantaneous acceleration.

 

 

                  18. A ball is thrown straight upwards, at the top of its path its velocity is zero and its acceleration is ___

a.

0 m/s2

c.

9.8 m/s2

b.

4.9 m/s2

d.

15.7 m/s2

 

 

                  19. An object falls freely in a vacuum on Earth, as it does so ___

a.

its velocity remains constant.

c.

.its acceleration remains constant.

b.

its velocity decreases

d.

acceleration decreases.

 

 

                  20. When a basketball player jumps to make a slam dunk the instant his feet leave the floor his acceleration ___

a.

depends on his launch speed.

c.

is 0 m/s2

b.

depends on the direction of his launch.

d.

is 9.8 m/s2

 

 

                  21. A ball is thrown straight up into the air, the time it takes the ball to go up ___

a.

is half the time it takes the ball to come back down.

c.

is twice the time it takes the ball to come back down.

b.

is the same as the time it takes the ball to come back down.

d.

is three quarters the time it takes the ball to come back down.

 

 

                  22. When a ball is thrown straight up into the air, the velocity with which it lands back in to the hand that threw it is ___ the velocity with which it left the hand that threw it.

a.

half of

c.

twice that of

b.

the same as

d.

three quarters that of

 

 

                  23. An object travels 3 m/s in the first second, 5 m/s during the second second, 7 m/s during the third second and so on. This means that the acceleration of the object is ___

a.

2 m/s2

c.

not uniflrm.

b.

6 m/s2

d.

not constant

 

 

                  24. An object is in free fall if ___

a.

one and only one force acts on an object and that one force is gravity.

c.

it is falling throuhg the air at terminal velocity.

b.

one and only one force acts on an object and that one vorce is air resistance.

d.

it is falling freely through the air prior to reaching terminal velocity.

 

 

                  25. Suppose you are driving a car that is going around a curve at a constant speed of 25 miles per hour. Which of these is true:

a.

Your speed is changing because you are turning.

c.

You are accelerating because you are changing direction.

b.

Your velocity is constant because you are not changing speed.

d.

Your dispalcement is constant because your motion is not in a straight line.

 

 

                  26. As an object falling through the air approches its terminal velocity which of these is true:

a.

Its acceleration remains constant.

c.

The distance it covers each second becomes less and less.

b.

Its velocity becomes nearly zero.

d.

The distance it covers each second is greater and greater.

Conceptual Physics Chapter 2: Linear Motion

Answer Section

 

PROBLEM

 

           1.     ANS:     

v = ? km/h                   v = d/t              v = 145 km / 2.5 h

d = 145 km                                          v = 58 km / h

t = 2.5 h

 

 

 

           2.     ANS:     

vi = 0 m/s                     a = vf - vi  / t                a = 27 m/s - 0 m/s / 6 s

vf = 27 m/s                   d = 1/2 at2                    a = 4.5 m/s2

t = 6 s                                                               d = 1/2 4.5 m/s2 (6 s)2

a) a = ? m/s2                                                     d = 2.25 m/s2 x 36 s2

b) d = ? m                                                        d = 81 m

 

 

 

 

 

 

 

 

 

 

 

           3.     ANS:     

d = 75 m                      d = 1/2 gt2                    t = Ö2(75 m) / 10 m/s2

g = 10 m/s2                   t = iÖ2d / g                   t = Ö150 m / 10 m/s2

a) t = ? s                       a = vf - vi / t                  t = Ö15 s2

b) vf = ? m                   vf = vi + at                    t = 3.9 s

                                                                        vf = 0 m/s + 10 m/s2 x 3.9 s

                                                                        vf =  39 m/s (This is nearly 90 mph!)             

 

SHORT ANSWER

 

           4.     ANS:     

Considering the SI unit for acceleration:

a) These are the SI units for acceleration: m/s2 and m/s/s.

b) Time appears twice in the SI unit for acceleration because time is used once for the rate of change in position and again for the rate of change in velocity.

 

           5.     ANS:     

Considering acceleration:

a) When you are accelerating you are either changing speed or you are changing direction.

b) It is possible to accelerate without changing speed by changing direction.

c) An example of an object that is accelerating without changing position is a rock thrown straight upwards. At the top of its trajectory the rock stops and changes direction without changing position.

 

           6.     ANS:     

a) This is a p-t graph of an object moving at constant velocity:

b) This is a v-t graph of an object undergoing uniform acceleration

 

TRUE/FALSE

 

           7.     ANS:      F

To calculate average speed you cannot ignore the parts of the trip when you were not moving, average speed requires total time as well as total distance.

 

           8.     ANS:      F

The slope of a line on a p-t graph tells you the velocity while the slope of the line on a v-t graph tells you acceleration.

 

           9.     ANS:      F

The SI unit for velocity as well as for speed is the m/s or the meter per second.

 

           10.   ANS:      T

 

           11.   ANS:      T

 

           12.   ANS:      F

The terms ‘velocity’ and ‘speed’ can not be used interchangeably because speed is a scalar and can be fully described as a magnitude while velocity is a vector and can only be fully described as a magnitude and a direction.

 

           13.   ANS:      T

 

           14.   ANS:      T

 

           15.   ANS:      F

When a car rounds a corner at constant speed it is accelerating because it is changing direction.

 

           16.   ANS:      F

As a rock falls freely its velocity increases, the distance the rock covers each second increases, but the acceleration remains constant.

 

MULTIPLE CHOICE

 

           17.   ANS:      A

 

           18.   ANS:      C

 

           19.   ANS:      C

 

           20.   ANS:      D

 

           21.   ANS:      B

 

           22.   ANS:      B

 

           23.   ANS:      A

           

 

           24.   ANS:      A

 

           25.   ANS:      C

 

           26.   ANS:      D