Solving Vector Questions: A Kangaroo's Journey

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In summary, the kangaroo was able to jump to a vertical height of 2.8m in 1.5s, and then reach the top in .76s.
  • #1
Amber
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Why can't I understand simple vector questions? I've just started a higher physics and that's what we're learning.

I'm stuck with this question:

A kangaroo was seen to jump to a vertical height of 2.8m. How long was it in the air?

I have the answer at the back of the book, but I don't know how to arrive at the answer! Please help!

Do I need to split it up into the components:

u - initial velocity
v - final velocity
a - acceleration
s - distance
t - time

I know the equations, but when I plug the numbers in, it doesn't come out as the right answer!

:confused:
 
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  • #2
is that all it says, must say how much Vi it has, or does it start from rest.
If it starts from rest you find the time it takes it to get to the top and then multiply by 2 and that's the total time, using the equation x=Vit + (1/2)at^2.
 
Last edited:
  • #3
two equations to be used here,
1>
Lets use the third kinematic eqn...
(using g down as positive sign so when direction of motion is upwards g is negative)
that gives us,
v^2=u^2-2gs

when it reaches maximum point , the final velocity becomes 0,
this gives v=0 and that gives us,
u^2 = 2gs
** we can calculate u since we know g and s

2>
now let's use the second kinematic equation,
s=ut+1/2at^2
from 1 we got 'u'
and we know a=-g and s=2.8
rearrange the equation and u get a quadratic in t
solve it to find t

But this t is the time to taken to reach the top we need the overall time which is just 2*t.

-- AI
 
  • #4
I guess your right, looks like I messed up :frown: . Gj though. One more thing how does the kangaroo manage to jump up and straight down?, he must land a little to the side or sometin.
 
  • #5
Why is that?
 
  • #6
nm, sometimes i don't even know what I am typing but I just type it. :tongue2:
 
  • #7
That's all the information I'm given.

The answer is 1.5s, and I still don't know how to reach it! :frown:
 
  • #8
Okay we have that
Vf=0 m/s
a=-9.81 m/s^2
x=2.8m

So in the equation

Vf^2 - Vi^2 = 2ax
0 - Vi^2 = 2 (-9.81)(2.8)
-Vi^2 = -54.936
Vi = 7.41m/s

Now in the equation

a = (Vi - Vf) / 2
-9.81 = (0-7.41) / t
-9.81t = -7.41
t = .76s

so that's only to the top so we multiply by 2, .76 * 2 = 1.52 s, which is the total time.
 
  • #9
cdhotfire said:
so that's only to the top so we multiply by 2, .76 * 2 = 1.52 s, which is the total time.

That's what I didn't do! I now understand why I have to multiply it by two, I didn't think about that earlier! Thank you so much. :smile:
 
  • #10
No problem, glad I could help yout out. :cool:
 

1. What are vectors and how are they used in solving problems?

Vectors are mathematical quantities that have both magnitude (size) and direction. They are commonly used in problem solving to represent physical quantities such as displacement, velocity, and force. Vectors are particularly useful for solving problems involving motion and forces.

2. How can I determine the magnitude and direction of a vector?

To determine the magnitude of a vector, you can use the Pythagorean theorem to find the length of the vector. The direction of a vector can be determined by calculating its angle relative to a reference axis or by using trigonometric functions. Alternatively, you can use the components of the vector to find its magnitude and direction.

3. What is the difference between a scalar and a vector?

A scalar is a quantity that has only magnitude, while a vector has both magnitude and direction. Examples of scalars include temperature, mass, and time, while examples of vectors include displacement, velocity, and force. Scalars are represented by single numbers, while vectors are represented by both magnitude and direction.

4. How can I add or subtract vectors?

In order to add or subtract vectors, you must first ensure that they are in the same coordinate system. Then, you can add or subtract the corresponding components of the vectors together to get the resulting vector. Graphically, you can use the parallelogram method or the head-to-tail method to add or subtract vectors.

5. How can I use vectors to solve real-world problems?

Vectors can be used to solve many real-world problems, such as determining the displacement and velocity of an object, finding the resultant force acting on an object, and analyzing the motion of projectiles. They can also be used in engineering, physics, and other fields to solve more complex problems involving forces and motion.

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