# Homework Help: Speed and velocity 4 quick questions

1. Oct 13, 2015

### Optikspik

1. If a block is moving at constant velocity, can the speed change? (yes or no question) I think the answer is no. Because The scalar quanitity of the speed will be the same as the velocity, but im not sure.

2. An ice hockey puck is being shot at with 150m/s , how long time does it take for it to move 10 meters. I dont understand the question, will there be any forces/ acceleration or something or just s=v/t?

3. Is acceleration a vector? I think i know this question it is yes, becuase u usually write a with an arrow above it.

4. Which two
Physical quantity is needed to determine average velocity, is it "distance" and "time" or what words do i wanna use there? And is "x" and"t" the only answer, or can "a" and "t" be an answer, or "v0" and "v_f" be an answer to this question?

Last edited by a moderator: Oct 13, 2015
2. Oct 13, 2015

### Staff: Mentor

Correct.
Speed and velocity are not the same, but if you don't change a vector, its magnitude won't change either.

Depends on the problem statement. A real hockey puck will certainly slow down, an idealized one for a problem might ignore friction.
It is.
Depends on the problem you are solving. If you know the total time and the total distance, you can calculate the average velocity, but that is not the only option.

3. Oct 13, 2015

### Optikspik

The question was only, which physics quanitites do you need to know to solve "average velocity" , more specifik which "two". My book says distance and time, but are there any else?

4. Oct 13, 2015

### haruspex

That is a sound basis for guessing it is a vector, but it is not the reason it is a vector. It is a vector because it is the change in velocity divided by time, velocity being a vector and time being a scalar. The difference of two vectors is a vector, and a vector divided by a scalar is a vector.
I would take distance to be a scalar, so no, this will not give you average velocity. The vector for change of position is usually called displacement.
See http://www.physicsclassroom.com/class/1DKin/Lesson-1/Distance-and-Displacement