OK, yesterday we looked at how fast an object will go a certain amount of time after being dropped, but what if we were to throw it? The formula form yesterday will work on something that gets thrown, but it only works to measure the speed straight up and down.
First let’s throw a grape down off the same building as yesterday. Let’s throw it at a speed of 5m/s downward (v0=-5m/s) and wait 3 seconds to measure its velocity (t=3).
First let’s throw a grape down off the same building as yesterday. Let’s throw it at a speed of 5m/s downward (v0=-5m/s) and wait 3 seconds to measure its velocity (t=3).
v=-5m/s+(-9.8m/s2•3s)
↓
v=-5m/s+(-29.4m/s)
↓
v=-34.4m/s
↓
v=-5m/s+(-29.4m/s)
↓
v=-34.4m/s
So 3 seconds after being thrown, the grape is falling at a speed of 34.4m/s. Next, we find a convenienly placed cannon on the roof of the building. There’s enough gunpowder in it to launch a watermelon straight up at a speed of 15m/s (v0=15m/s). Let’s launch the watermelon and measure its velocity after 2 seconds (t=2s).
v=15m/s+(-9.8m/s2•2s)
↓
v=15m/s+(-19.6m/s)
↓
v=-4.6m/s
↓
v=15m/s+(-19.6m/s)
↓
v=-4.6m/s
So when we measured the melon’s velocity 2 seconds after launching it, it was already starting to come back down and was moving at 4.6m/s downward.
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