How do you find the initial velocity of a projectile given angle/distance?

In summary: Just for the record, the initial velocity can be found directly from the horizontal component of the motion, as it is constant. In summary, the problem can be solved by identifying the relevant variables and using the appropriate equations from the SUVAT set.
  • #1
iamcgettigan
2
0
Homework Statement
I am in 10th grade physics. The question is: A person standing on top of a 30.0 m high building throws a ball with an angle of 20.0° below horizontal. If the ball lands 29.3 m away from the building, what is the initial velocity of the ball? I know the answer is 16m/s, however I am unsure of how to arrive at this answer.
Relevant Equations
s=ut+½at^2
I tried resolving the information given into vertical and horizontal components. I then tried to find time, as this is how I would find the initial velocity. However, I am unsure of how to use the angle in this problem to help solve it. I am also unsure of how to find the initial velocity only given angle and distances. Any help would be greatly appreciated!
 
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  • #2
iamcgettigan said:
Homework Statement:: I am in 10th grade physics. The question is: A person standing on top of a 30.0 m high building throws a ball with an angle of 20.0° below horizontal. If the ball lands 29.3 m away from the building, what is the initial velocity of the ball? I know the answer is 16m/s, however I am unsure of how to arrive at this answer.
Relevant Equations:: s=ut+½at^2

I tried resolving the information given into vertical and horizontal components. I then tried to find time, as this is how I would find the initial velocity. However, I am unsure of how to use the angle in this problem to help solve it. I am also unsure of how to find the initial velocity only given angle and distances. Any help would be greatly appreciated!
Please post your work as far as you get (and please, not as an image).

In the standard form of constant acceleration equations (SUVAT) there are five variables. Each equation relates four of them, so five equations for vertical motion. Horizontal is somewhat simpler.

The trick is to identify those variables which are of interest and choose your equations accordingly. Any variable you are given in the question and any variable you are asked to find is of interest. A variable which connects the horizontal and vertical motions (there is one here) is also relevant.
 
  • #3
haruspex said:
Please post your work as far as you get (and please, not as an image).

In the standard form of constant acceleration equations (SUVAT) there are five variables. Each equation relates four of them, so five equations for vertical motion. Horizontal is somewhat simpler.

The trick is to identify those variables which are of interest and choose your equations accordingly. Any variable you are given in the question and any variable you are asked to find is of interest. A variable which connects the horizontal and vertical motions (there is one here) is also relevant.

Thank you for your response. I am sorry to have somewhat wasted your time as I have figured it out. Thanks again.
 
  • #4
iamcgettigan said:
Thank you for your response. I am sorry to have somewhat wasted your time as I have figured it out. Thanks again.
That's fine - glad you got there by your own efforts.
 

FAQ: How do you find the initial velocity of a projectile given angle/distance?

How do you calculate the initial velocity of a projectile given the angle and distance?

The initial velocity of a projectile can be calculated using the formula v0 = d / (t * cosθ), where v0 is the initial velocity, d is the distance traveled, t is the time of flight, and θ is the angle of launch.

Can the initial velocity be negative?

Yes, the initial velocity can be negative if the projectile is launched downward or in the opposite direction of the positive direction of the coordinate system.

How does the angle of launch affect the initial velocity?

The angle of launch affects the initial velocity by changing the vertical and horizontal components of the velocity. The higher the angle, the greater the vertical component and the lower the horizontal component of the initial velocity.

Do I need to consider air resistance when calculating the initial velocity?

In most cases, air resistance can be ignored when calculating the initial velocity of a projectile. However, if the projectile is traveling at high speeds or over long distances, air resistance may have a noticeable effect on the initial velocity and should be taken into account.

Is the initial velocity the same as the average velocity?

No, the initial velocity and average velocity are not the same. The initial velocity is the velocity of the projectile at the moment it is launched, while the average velocity is the average of all the velocities during the entire flight of the projectile.

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