# I can not calculate the displacement

• maro_toni
In summary, displacement is the change in position of an object and is crucial in understanding its motion and direction. To calculate displacement, the initial and final positions of the object are needed, and it is typically measured in units of length. Some common causes of not being able to calculate displacement include lack of information or understanding. Displacement can be negative if the object moves in the opposite direction of its initial point.
maro_toni
Hello,

Q1-If you move 10 km North, 10 km East, and 10 km South,

a. What is your displacement? [ can not calculate it ]

b.What is the total distance you traveled? [30 km ]

2. The below graph represents the position of a mouse at a given time.
http://library.thinkquest.org/10796/ch2/Img00007.gif"

a. What is the average velocity between t = 0 to t = 4? [10 m/s]

b. What is the distance you traveled from t = 3 to t = 7? [ can not calculate it ]

c. What is the total displacement? [ can not calculate it ]

3. Answer the questions using the following graph.
http://library.thinkquest.org/10796/ch2/Img00008.gif"

a. What is the distance it traveled between t = 0 to t = 2? [20]

b. What is the instantaneous velocity when t = 4? [ can not calculate it ]

4. Jack and Michael are both running together at constant velocity of 10 m/s.

a. What is Jack's relative velocity to Michael? [10 i think ... but it's wrong]
b. What is Michael's relative velocity to Jack?

5. A rat and a cat are 25 m apart. When the rat started to run at 2 km/h, the cat started to chase him at 10 km/h. Can the cat catch the rat in 10 seconds?
YES??

i think each have a role (( equation )) but I cann't find them...

Thank You. =)

Last edited by a moderator:
maro_toni said:
Q1-If you move 10 km North, 10 km East, and 10 km South,

a. What is your displacement? [ can not calculate it ]

Draw a picture and it should be obvious.

2. The below graph represents the position of a mouse at a given time.
http://library.thinkquest.org/10796/ch2/Img00007.gif"

a. What is the average velocity between t = 0 to t = 4? [10 m/s]

Correct. (Sorry, previously I had said this was incorrect.)

b. What is the distance you traveled from t = 3 to t = 7? [ can not calculate it ]

c. What is the total displacement? [ can not calculate it ]

What's the relationship between displacement and velocity? Once you answer this fundamental question this is a very easy problem.

3. Answer the questions using the following graph.
http://library.thinkquest.org/10796/ch2/Img00008.gif"

a. What is the distance it traveled between t = 0 to t = 2? [20]

The method you used to do this problem is the same you'd use for (b) and (c) in the previous problem.

b. What is the instantaneous velocity when t = 4? [ can not calculate it ]

Just look at the graph??

4. Jack and Michael are both running together at constant velocity of 10 m/s.

a. What is Jack's relative velocity to Michael? [10 i think ... but it's wrong]

10 m/s is incorrect. Re-read the question.

5. A rat and a cat are 25 m apart. When the rat started to run at 2 km/h, the cat started to chase him at 10 km/h. Can the cat catch the rat in 10 seconds?
YES??

How do you know? Figure out how far the rat and cat travel in 10 seconds at their respective velocities. Mind your units.

Last edited by a moderator:
fss said:
maro_toni said:
a. What is the average velocity between t = 0 to t = 4? [10 m/s]
Incorrect.

Really? Why? Average velocity is defined to be the total distance traveled divided by the time it took to cover that distance. At time t=0, the mouse had traveled 0 m. At time t=4, the mouse had covered 40 m. So,

$$V_{avg} = \frac{(40 - 0)m}{(4-0)s} = 10 m/s$$

maro_toni said:
4. Jack and Michael are both running together at constant velocity of 10 m/s.

a. What is Jack's relative velocity to Michael? [10 i think ... but it's wrong]
b. What is Michael's relative velocity to Jack?

Think of Jack and Michael both sitting in the same car, which is traveling at 10m/s. From Jack's perspective (compared to Jack), how fast is Michael moving?

maro_toni said:
5. A rat and a cat are 25 m apart. When the rat started to run at 2 km/h, the cat started to chase him at 10 km/h. Can the cat catch the rat in 10 seconds?

I'm sure the intent of this question is to say that when the rat started running, it headed directly away from the cat (not towards, or at some other angle).
It is also assumed that there is no acceleration; the rat instantly is moving at 2 km/h and the cat is instantly moving at 10 km/h.

Also, note that we are dealing with several units here:

The distance between the rat and cat is given in meters.
Theirs speeds are given in kilometers per hour.
The time is given in seconds.

You should not only be able to determine if the cat can reach the cat in 10 sec, but exactly how long it would it would take for the cat to reach the rat, as well as how far each traveled before the cat had dinner.

zgozvrm said:
Really? Why? Average velocity is defined to be the total distance traveled divided by the time it took to cover that distance. At time t=0, the mouse had traveled 0 m. At time t=4, the mouse had covered 40 m. So,

$$V_{avg} = \frac{(40 - 0)m}{(4-0)s} = 10 m/s$$

Oops, I misread that one. You are correct, thanks for pointing that out.

fss said:
Oops, I misread that one. You are correct, thanks for pointing that out.

(Hey, it happens to all of us sometime!)

No problem ... you actually had me thinking that I didn't know what I was doing!

## 1. What is displacement and why is it important to calculate it?

Displacement is the change in position of an object from its initial position to its final position. It is important to calculate displacement because it helps us understand the motion and direction of an object, and it is a crucial factor in determining an object's velocity and acceleration.

## 2. How do you calculate displacement?

To calculate displacement, you need to know the initial position and final position of the object. Subtract the initial position from the final position to get the distance the object has moved. The direction of displacement can be determined by the sign of the distance (positive for forward, negative for backward).

## 3. What units are used to measure displacement?

Displacement is typically measured in units of length, such as meters (m) or centimeters (cm). However, it can also be measured in other units if necessary, such as feet (ft) or inches (in).

## 4. What are some common causes of not being able to calculate displacement?

Some common causes of not being able to calculate displacement include not having enough information about the object's initial and final positions, not using the correct units for measurement, or not understanding the concept of displacement. It is important to have all necessary information and a clear understanding of the concept in order to accurately calculate displacement.

## 5. Can displacement ever be negative?

Yes, displacement can be negative. As displacement is the change in position from an initial point to a final point, the direction of the displacement can be either positive or negative depending on the movement of the object. A negative displacement indicates that the object has moved in the opposite direction of the initial point.

• Introductory Physics Homework Help
Replies
17
Views
1K
• Introductory Physics Homework Help
Replies
5
Views
1K
• Introductory Physics Homework Help
Replies
2
Views
325
• Introductory Physics Homework Help
Replies
5
Views
1K
• Introductory Physics Homework Help
Replies
3
Views
1K
• Introductory Physics Homework Help
Replies
11
Views
2K
• Introductory Physics Homework Help
Replies
5
Views
979
• Introductory Physics Homework Help
Replies
11
Views
902
• Introductory Physics Homework Help
Replies
15
Views
1K
• Introductory Physics Homework Help
Replies
5
Views
2K