Projectiles why the person multiplied the column vector OB by h?

In summary, the person multiplied the column vector OB by h because the velocity vector must be a constant times the displacement vector in order for them to have the same slope and be parallel. The h represents the units and is used to solve for the time t. The steps can also be solved using the slope of OB and the slope of the trajectory at time t.
  • #1
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Question 7c on attached,

in the solutions could someone explain why the person multiplied the column vector OB by h? I don't get it
 

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  • #2


I'm glad you said it was an "h"; looked like a "u" to me which would really be mysterious.
He is just saying the velocity vector must be a constant times the displacement vector OB. Same as saying the ratio of the vertical to the horizontal must be the same for the displacement and the velocity in order for them to have the same slope and be parallel. The h just takes care of the units so h*(50 meters) = 10 m/s
Funny, the h doesn't seem to be used in the following steps. I would have followed up the
velocity vector = [Vx,Vy] = h[50, -52.5]
with [10, 14 - gt] = [50h, -52.5*50h]
and then 10 = 50h so h = 0.2 and 14 - gt = -52.5*50h
which solves to t = 2.5.

Alternatively, slope of OB = = slope of trajectory at time t
Dy/Dx = Vy/Vx
-52.5/50= (14- gt)/10
-525/50 = 14 - gt
gt = 14 +525/50 = 24.5
t = 24.5/g = 2.50.
 
  • #3


The velocity vector must be parallel to OB.
 
  • #4


Delphi51 said:
I'm glad you said it was an "h"; looked like a "u" to me which would really be mysterious.
He is just saying the velocity vector must be a constant times the displacement vector OB. Same as saying the ratio of the vertical to the horizontal must be the same for the displacement and the velocity in order for them to have the same slope and be parallel. The h just takes care of the units so h*(50 meters) = 10 m/s
Funny, the h doesn't seem to be used in the following steps. I would have followed up the
velocity vector = [Vx,Vy] = h[50, -52.5]
with [10, 14 - gt] = [50h, -52.5*50h]
and then 10 = 50h so h = 0.2 and 14 - gt = -52.5*50h
which solves to t = 2.5.

Alternatively, slope of OB = = slope of trajectory at time t
Dy/Dx = Vy/Vx
-52.5/50= (14- gt)/10
-525/50 = 14 - gt
gt = 14 +525/50 = 24.5
t = 24.5/g = 2.50.

cheers
 
  • #5

The person most likely multiplied the column vector OB by h in order to account for the height of the projectile. This is a common practice in projectile motion problems, where the vertical component of the vector is multiplied by the time of flight (h = gt) to calculate the maximum height of the projectile. This is because the vertical position of the projectile is affected by gravity, which is dependent on time. By multiplying the vertical component by time, the person is able to accurately calculate the height of the projectile at any given time during its flight.
 

1. Why did the person multiply the column vector OB by h?

The person likely multiplied the column vector OB by h to calculate the vertical displacement of the projectile. By multiplying the magnitude of OB by h, they can determine how far the projectile has traveled vertically.

2. What does the column vector OB represent in projectile motion?

The column vector OB represents the initial velocity of the projectile. It contains both the magnitude and direction of the initial velocity, which is essential in determining the trajectory of the projectile.

3. How does multiplying the column vector OB by h help in calculating the trajectory of the projectile?

Multiplying the column vector OB by h allows for the calculation of the vertical displacement of the projectile. This information, along with the initial velocity, can help determine the height, range, and flight time of the projectile.

4. Is it necessary to consider the vertical displacement in projectile motion?

Yes, it is essential to consider the vertical displacement in projectile motion. The vertical displacement affects the trajectory and flight time of the projectile and is necessary to accurately calculate the overall motion of the projectile.

5. Can the column vector OB be multiplied by any other value besides h?

Yes, the column vector OB can be multiplied by any value, as long as it is used consistently throughout the calculation. For example, it could be multiplied by time to determine the horizontal displacement of the projectile.

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