Question from a Physics beginner

[SnackMan78]

Hi all,

I am just beginning Physics, and have 2 simple problems but don't know how to go about solving them. Here goes:

1) An eagle is flying due east at 8.9 m/s carrying a gopher in its talons. The gopher manages to break free at a height of 12 m. What is the magnitude of the gophers velocity as it reaches the ground?

What formula is used to do to calculation? This is a multiple choice question, but using the Pythagorean Theorem doesn't yield any of the choices.

The choices: 8.9 m/s, 9.8 m/s, 11 m/s 18 m/s or 22 m/s?

2) A projectile is fired from a gun and has initial horizontal and vertical components of velocity equal to 30 m/s and 40 m/s, respectively. Determine the initial speed of the projectile.

Again, what formula is used to do to calculation?

 

[HallsofIvy]

Hi all,

I am just beginning Physics, and have 2 simple problems but don't know how to go about solving them. Here goes:

1) An eagle is flying due east at 8.9 m/s carrying a gopher in its talons. The gopher manages to break free at a height of 12 m. What is the magnitude of the gophers velocity as it reaches the ground?

What formula is used to do to calculation? This is a multiple choice question, but using the Pythagorean Theorem doesn't yield any of the choices.

Well, of course, it wouldn't. The Pythagorean theorem doesn't have any thing to do with kinematics- and the gopher's fall will not be a straight line.
Do you know any formulas connecting velocity and distance to time when you have a constant acceleration? Do you know what the acceleration due to gravity is?

The choices: 8.9 m/s, 9.8 m/s, 11 m/s 18 m/s or 22 m/s?

2) A projectile is fired from a gun and has initial horizontal and vertical components of velocity equal to 30 m/s and 40 m/s, respectively. Determine the initial speed of the projectile.

Again, what formula is used to do to calculation?

Exactly the same formulas you used in (1)! You should have one formula for vertical motion involving "g" (the acceleration due to gravity) and one for horizontal motion with no acceleration.

 

[Grogs]

Hi all,

I am just beginning Physics, and have 2 simple problems but don't know how to go about solving them. Here goes:

1) An eagle is flying due east at 8.9 m/s carrying a gopher in its talons. The gopher manages to break free at a height of 12 m. What is the magnitude of the gophers velocity as it reaches the ground?

What formula is used to do to calculation? This is a multiple choice question, but using the Pythagorean Theorem doesn't yield any of the choices.

The choices: 8.9 m/s, 9.8 m/s, 11 m/s 18 m/s or 22 m/s?

Look at what you're asked to find here. In this case, they're asking to find the magnitude of the gopher's velocity when he hits the ground. Let's call this v_{f}. In order to find the final velocity, v_{f}, you'll need to find the two components, v_{xf} and v_{yf}. These two components are related to v_{f} by the Pythagorean theorem:

v_{f}^2=v_{xf}^2 + v_{yf}^2

Now, look at what you've got. If you set the direction the eagle is flying to be +x and the direction of gravity to be +y, you can see you have v_{ix} = 8.9 m/s given to you. You're also given that the gopher falls 12 meters, so y_{i} = 0 m and y_{f} = 12 m. At this point, there are 3 things you need to do to solve the equation:

1) Find v_{xf} from what you know about v_{xi}.
2) Find v_{yf} from what you know about y_{i} and y_{f}. This is where your kinematics equations come in.
3) Once you've solved for v_{xf} and v_{yf}, solve for v_{f} using the pythagorean theorem.

The answer I come up with is one of the choices above.

2) A projectile is fired from a gun and has initial horizontal and vertical components of velocity equal to 30 m/s and 40 m/s, respectively. Determine the initial speed of the projectile.

Again, what formula is used to do to calculation?

No kinematics involved here. You're simply given the two components of the initial velocity and asked to find the initial speed, i.e., the magnitude of the initial velocity. Use the Pythogorean Theorem and solve for v_{i} like step 3 above.