# 70 Unit 7 Practice and Assessment

**Outcome 1**

1) Explain the difference between distance and displacement.

2) Explain how velocity relates to position and how acceleration relates to velocity.

**Outcome 2**

3) An object is thrown into the air and then caught. Assume the speed is slow enough that air resistance is negligible.

a) How much speed does the object lose each second on the way up?

b) What is the speed at the peak height?

c) How much speed does the object gain each second as it falls back down?

d) Are the starting and finishing speeds the same?

e) Are the starting and finishing velocities the same?

4) Calculate the drag force on a swimmer moving through water at 0.75 **m/s***. * The drag coefficient for a human in the prone position is roughly 0.25. Look up the density of water in standard units and cite your source. Estimate the cross-sectional area of a human for this situation by using your own body or average human body measurements (cite your source).

5) The swimmer above is moving at a constant speed. What is the size and direction of the average force applied to the swimmer by the water due to their swimming motion?

**Outcome 3**

6) A toddler runs away from a parent at 0.3 **m/s** for 3 **s**, stops for 2 **s** to see if they are being chased.

a) Draw a velocity vs. time graph for the toddler’s motion

b) Draw an acceleration vs. time graph for the toddler’s motion

c) Draw a position vs. time graph for the toddler’s motion (you will need to calculate the displacements that occur during each interval in order to draw this graph).

7) Upon realizing they might be chased after the 2 **s** stop, the toddler from the previous exercise begins slowly walking away and increasing speed into a run, reaching a speed of 0.4 **m/s** only 3 **s** later.

a) Complete the acceleration vs. time graph for the toddler’s motion, now including this new motion. You may draw a new graph or add to your previous graph in a different color. (You will need to calculate the acceleration during this last part of the toddler’s motion in order to complete this graph).

b) Complete the velocity vs. time graph for the toddler’s motion. You may draw a new graph or add to your previous graph in a different color. (You will need to use the acceleration you found above to calculate a change in velocity to complete this graph).

c) Complete the position vs. time graph for the toddler’s motion. You may draw a new graph or add to your previous graph in a different color. (You will need to use the acceleration you found above to calculate displacements to complete this graph).

8) Describe the motion depicted by the following velocity vs. time graph. The vertical axis tick marks indicate 1 **m/s** intervals, starting from zero **m/s** at the horizontal axis.

9) Draw the acceleration vs. time graph associated with the velocity vs time graph above.

10) Draw the position vs. time graph associated with the previous velocity and acceleration vs. time graphs.

**Outcome 4**

11) A person with mass of 65 **kg **is out walking two dogs when suddenly the dogs pull in opposite directions. Dog 1 pulls with a force of 500 **N** to the right. Dog 2 pulls with 300 **N** to the left. In order to stay upright, the person has to run to keep their feet underneath their center of gravity (rather than just keep them planted). Therefore, we will ignore friction.

a) Draw a free body diagram of the dog walker. Don’t forget to include directions with forces, accelerations, and velocities when answering the following questions.

b) What is the net force on the dog walker?

c) What is the acceleration of the dog walker?

d) What is the velocity of the dog walker after **3 s**?

e) What is the average velocity of the dog walker during this **3 s **period.

f) What distance will the dog walker have moved in 3 **s**?

- Velocity Graph Uploaded by Riaan at English Wikibooks and transferred from en.wikibooks to Commons., GFDL, is licensed under CC BY-NC-SA 4.0 ↵

small enough as to not push the results of an analysis outside the desired level of accuracy

a force applied by a fluid to any object moving with respect to the fluid, which acts opposite to the relative motion of the object relative to the fluid

lying horizontally with the face and torso facing down

relation between the amount of a material and the space it takes up, calculated as mass divided by volume.

The cross-sectional area is the area of a two-dimensional shape that is obtained when a three-dimensional object - such as a cylinder - is sliced perpendicular to some specified axis at a point. For example, the cross-section of a cylinder - when sliced parallel to its base - is a circle

not changing, having the same value within a specified interval of time, space, or other physical variable

distance traveled per unit time

a quantity of speed with a defined direction, the change in speed per unit time, the slope of the position vs. time graph

the change in velocity per unit time, the slope of a velocity vs. time graph

location in space defined relative to a chosen origin, or location where the value of position is zero

change in position, typically in reference to a change away from an equilibrium position or a change occurring over a specified time interval

a measurement of the amount of matter in an object made by determining its resistance to changes in motion (inertial mass) or the force of gravity applied to it by another known mass from a known distance (gravitational mass). The gravitational mass and an inertial mass appear equal.

a graphical illustration used to visualize the forces applied to an object

the total amount of remaining unbalanced force on an object