To understand how the trajectory of an object depends on its initial velocity, a

Question

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).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. First, you will investigate purely vertical motion. The kinematics equation for vertical motion (ignoring air resistance) is given by y(t)=y0+v0t(1/2)gt2, where y0=0 is the initial position (which is 1.2 m above the ground due to the wheels of the cannon), v0 is the initial speed, and g is the acceleration due to gravity. Shoot the baseball straight upward (at an angle of 90) with an initial speed of 20 m/s. How long does it take for the baseball to hit the ground?

Explanation / Answer

time taken to hit the ground = 2u/g = 2 x 20/9.8 = 4.0816 seconds

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