physics

PHYS 1401 Lab-01: Projectile Motion

Name: ___________________________

Objectives:

· To understand how the trajectory of an object depends on its initial velocity, and to understand how air resistance affects the trajectory.

· Understand the relationship that launch angle plays with projectile motion.

Open PhET simulation: https://phet.colorado.edu/sims/html/projectile-motion/latest/projectile-motion_en.html

1. Start the simulation by selecting the option labeled “Intro”.

2. Press the red fire icon to launch an object.

3. You can choose the object by clicking on one of the objects in the scroll-down menu at top right.

4. To adjust the cannon barrel’s angle, click and drag on it.

5. You can also adjust the initial speed of the object using the toolbar at the bottom left.

6. To measure the height, range, or hang time, drag the box that contains these quantities from the top of the screen to various points of interest along the object’s trajectory.

7. Play around with the simulation. When you are done, click the Erase icon and set the object to a pumpkin prior to beginning to Activity 1.

Activity-1

First, you will investigate purely vertical motion. The kinematics equation for vertical motion (ignoring air resistance) is given by

Where y0 = 0 is the initial position, v0 is the initial speed, and g is the acceleration due to gravity.

Drag the cannon downwards so it is at ground level or 0 m (which represents the initial height of the object), then fire the pumpkin straight upward (at an angle of 90) with an initial speed of 14 m/s.

Question-1: How long does it take for the pumpkin to hit the ground?

The time value could be determined from the kinematics equation. Given that the initial and final height of the pumpkin is 0 m, the kinematics equation becomes

This calculation is interesting because it shows that for vertical motion, the time the pumpkin is in the air is proportional to its initial speed.

Question-2: When the pumpkin is shot straight upward with an initial speed of 14 m/s, what is the maximum height above its initial location? Show your calculation using kinematics equation.

Question-3: If the initial speed of the pumpkin is doubled, how does the maximum height change?

Question-4: When the projectile is moving vertically upward, what is the direction of velocity and acceleration?

Erase all the trajectories, and fire the pumpkin vertically again with an initial speed of 14 m/s. The maximum height is 9.99 m as found earlier. If the pumpkin isn’t fired vertically but at an angle less than 90, it can reach the same maximum height if its initial speed is faster. Set the initial speed to 22 m/s and find the angle such that the maximum height is roughly the same.

Question-5: What is the angle?

The pumpkin launched at this angle reaches the same height as the vertically launched pumpkin because they have the same initial speed in the initial direction. The initial speed in the vertical direction is given by v0sinq.

Question-6: When the pumpkin is launched at an angle, do the components of velocity and acceleration change during the flight of pumpkin? If not, which quantity remains constant?

Question-7: The figure below shows two trajectories, made by two pumpkins launched with different angles and possibly different initial speeds.

Based on the figure, for which trajectory was the pumpkin in the air for the greatest amount of time?

Activity-2

In this experiment, we will change the angle of a cannon and see how it affects the distance a pumpkin will travel.

1. Select Lab icon.

2. Use the data table to determine what angle the cannon should be placed.

3. After you fire the pumpkin, measure the distance the pumpkin flew. Drag the crosshairs marked with time and range to the spot where the pumpkin landed. Place the circle the left of the blue box at the spot where pumpkin landed.

4. Record the distance the pumpkin travels in Table-1. Round to the nearest tenth place.

5. Select a different projectile like car from the dropdown box on the right. Repeat the above process.

The range is the horizontal distance from the cannon when the pumpkin hits the ground. This distance is given by the product of horizontal velocity (which is constant) and the amount of time the pumpkin is in the air (which is determined by the vertical component of the initial velocity, as you just discovered).

2nd Projectile = ______________

Table-1

Initial Angle	Time (in seconds)	Range of pumpkin (in meters)	Range of 2nd projectile (in meters)
25º
35º
45º
55º
65º
75º

Question-8: What angle gave the most distance?

a) Pumpkin?

b) Other object? (Identify your projectile)

Question-9: Which angle gave the least distance?

a. Pumpkin?

b. Other projectile?

Question-10: Does the trajectory depend on the mass of the projectile if we ignore air resistance?

Question-11: Explain how the launch angle impacts projectile distance in few sentences.

Question-12: What should be the launch angle so that the pumpkin lands on the man’s statue. Show your calculations. Perform the experiment and upload the screenshot.

Click the eraser button. Set your launch angle to 75°. The default velocity for your prior simulation was 18 m/s. Change the velocity as directed and complete the Table-2.

Table-2

Velocity	Range of cannon ball (in meters)	Range of 2nd projectile (in meters)
10 m/s
15 m/s
18 m/s
20 m/s
25 m/s

Question-13: Explain the role that velocity has with projectile motion in few sentences.

Reset the velocity to 18 m/s and change the canon base height from 0 m to 15 m above the ground. Fire several pumpkins while varying the angle.

Question-14: For what angle is the range the greatest?

Question-15: Explain what happens when you change the height from which you launch a projectile?

Question-16: If a light mass and a heavy mass are launched at the same angle with same velocity, which mass will reach the ground first?

Set the launch angle to 45° and click on the “air resistance” Set the drag coefficient to 0.47.

Question-17: How did air resistance affect the range of the projectile?

Conclusion: Write at least 3 sentences explaining in detail what factors affect the distance of a projectile travel and how.