Meaning of: Indicate magnitude & direction of all vectors

[Player7900]

Meaning of: "Indicate magnitude & direction of all vectors"

I don't actually need help solving this problem I am working on, as I already have the answers. What I need help with is understanding this phrase: "Include both magnitude & direction of all vectors" --- What does this mean?

Here is the question and its answers:

Question: A ball is thrown straight upward - it is traveling at 50 m/s at the moment it is thrown. Ignoring air resistance, and rounding the force of gravity to 10 m/s:

(1) How long will it take for the ball to stop rising?
(2) How far will the ball have traveled during this time?
(3) What is the ball's acceleration during this time?

Answers:

(1) 2.5 seconds
(2) 125 metres
(3) -20 m/s²

So, if someone could tell me what the "magnitude & direction of vectors" are, it would be greatly appreciated

 

[matt_crouch]

Velocity and displacement for example are vectors. Vectors have both magnitude and direction opposed to scalers which have purely magnitude. You basically have got to say which direction it is acting in so for example if a ball is thrown upwards the force of gravity acts in the opposite direction so it would be negative against the direction of the ball.

Also you need to check your answers i believe =]
show your working so we can see where you have made a mistake.

 

[Player7900]

Velocity and displacement for example are vectors. Vectors have both magnitude and direction opposed to scalers which have purely magnitude. You basically have got to say which direction it is acting in so for example if a ball is thrown upwards the force of gravity acts in the opposite direction so it would be negative against the direction of the ball.

Also you need to check your answers i believe =]
show your working so we can see where you have made a mistake.

Here is my work. (Remember that in the question it says, force of gravity may be rounded to 10m/s)

DISTANCE:

1/2mv² = mgh [Mass cancels itself out]
1/2v² = gh
--------------------------------------------------
1/2(50²) = 10h
1/2(2500) = 10h
1250 = 10h
1250/10 = h
125 = h


TIME:

t = d/v
-----------
t = 125/50
t = 2.5


ACCELERATION

a = v2-v1/t
------------
a = 0-50/2.5
a = (-50)/2.5
a = (-20)

 

[Player7900]

Velocity and displacement for example are vectors. Vectors have both magnitude and direction opposed to scalers which have purely magnitude. You basically have got to say which direction it is acting in so for example if a ball is thrown upwards the force of gravity acts in the opposite direction so it would be negative against the direction of the ball.

Also you need to check your answers i believe =]
show your working so we can see where you have made a mistake.

Regarding the vectors:

Is it enough then to write the answer for the distance question as "The ball has traveled 125 metres upward by the time it stopped rising" --- or am I missing something?

 

[matt_crouch]

ahhh i see where u have made the mistake remember that when the ball is thrown upwards it is still under the influence of gravity so you can't use v=s/t because that assumes that the object isn't accelerating and it is in fact decelerating, gravity is slowing the ball down.For part C its the right method but the acceleration is still due to gravity so you don't actually have to do any calculations.
With the vectors I am sure that is fine. With Part C try and think of the ball working against gravity so its slowing the ball down. So the acceleration is acting in the opposite direction of movement

 

[Player7900]

ahhh i see where u have made the mistake remember that when the ball is thrown upwards it is still under the influence of gravity so you can't use v=s/t because that assumes that the object isn't accelerating and it is in fact decelerating, gravity is slowing the ball down.For part C its the right method but the acceleration is still due to gravity so you don't actually have to do any calculations.
With the vectors I am sure that is fine. With Part C try and think of the ball working against gravity so its slowing the ball down. So the acceleration is acting in the opposite direction of movement

So are you saying that for Part C, the acceleration is simply (-10m/s²) since that is the force of gravity pushing down on the ball?

 

[matt_crouch]

yes =]