# Problem: To understand how the trajectory of an object depends on its initial velocity, and to understand how air resistance affects the trajectory. For this problem, use the PhET simulation Projectile Motion. This simulation allows you to fire an object from a cannon, see its trajectory, and measure its range and hang time (the amount of time in the air). Click to launch video simulation Start the simulation. Press Fire to launch an object. You can choose the object by clicking on one of the objects in the scroll-down menu at top right (a cannonball is not among the choices). To adjust the cannon barrel’s angle, click and drag on it or type in a numerical value (in degrees). You can also adjust the speed, mass, and diameter of the object by typing in values. Clicking Air Resistance displays settings for (1) the drag coefficient and (2) the altitude (which controls the air density). For this tutorial, we will use an altitude of zero (sea level) and let the drag coefficient be automatically set when the object is chosen. Play around with the simulation. When you are done, click Erase and select a baseball prior to beginning Part A. Leave Air Resistance unchecked. In the previous part, you discovered that the trajectory of an object does not depend on the object’s size or mass. But if you have ever seen a parachutist or a feather falling, you know this isn’t really true. That is because we have been neglecting air resistance, and we will now study its effects here. Select Air Resistance for the simulation. Fire a baseball with an initial speed of roughly 20 m/s and an angle of 45∘. Compare the trajectory to the case without air resistance. How do the trajectories differ? The trajectory with air resistance has a shorter range.The trajectory with air resistance has a longer range.The trajectories are identical.

###### FREE Expert Solution

Range:

$\overline{){\mathbf{R}}{\mathbf{=}}{{\mathbf{v}}}_{\mathbf{0}\mathbf{,}\mathbf{x}}{\mathbf{t}}{\mathbf{=}}{{\mathbf{v}}}_{{\mathbf{0}}}{\mathbf{s}}{\mathbf{i}}{\mathbf{n}}{\mathbf{\theta }}{\mathbf{·}}{\mathbf{t}}}$

In the previous examples, we assumed a constant horizontal velocity. However, in the presence of air resistance, the horizontal velocity decreases with time. Consequently, the range decreases.

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###### Problem Details

To understand how the trajectory of an object depends on its initial velocity, and to understand how air resistance affects the trajectory. For this problem, use the PhET simulation Projectile Motion. This simulation allows you to fire an object from a cannon, see its trajectory, and measure its range and hang time (the amount of time in the air). Click to launch video simulation Start the simulation. Press Fire to launch an object. You can choose the object by clicking on one of the objects in the scroll-down menu at top right (a cannonball is not among the choices). To adjust the cannon barrel’s angle, click and drag on it or type in a numerical value (in degrees). You can also adjust the speed, mass, and diameter of the object by typing in values. Clicking Air Resistance displays settings for (1) the drag coefficient and (2) the altitude (which controls the air density). For this tutorial, we will use an altitude of zero (sea level) and let the drag coefficient be automatically set when the object is chosen. Play around with the simulation. When you are done, click Erase and select a baseball prior to beginning Part A. Leave Air Resistance unchecked.

In the previous part, you discovered that the trajectory of an object does not depend on the object’s size or mass. But if you have ever seen a parachutist or a feather falling, you know this isn’t really true. That is because we have been neglecting air resistance, and we will now study its effects here. Select Air Resistance for the simulation. Fire a baseball with an initial speed of roughly 20 m/s and an angle of 45∘. Compare the trajectory to the case without air resistance. How do the trajectories differ?

1. The trajectory with air resistance has a shorter range.
2. The trajectory with air resistance has a longer range.
3. The trajectories are identical.