HardPhysicsHigh School (11–12)Mechanics › Vectors and Motion in a PlaneConceptualBoard ExamAPA-LevelIB
Two identical balls are 20 m above level ground…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Two identical balls are above level ground. At the same moment, one is dropped and the other is thrown horizontally at . Ignore the air, and take .
- Which ball lands first?
- How fast is each ball moving just before it lands?
Need a reminder? The key ideaShow
The vertical motion does not depend on the horizontal motion. A ball that starts with no vertical velocity falls a height in , however fast it moves sideways.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Time. For both balls, . They land together.
Step 2. The dropped ball. , straight down.
Step 3. The thrown ball. down and , so .
Answer: (a) They land together, after . (b) and .
Watch out. "It moves faster, so it lands sooner" and "it goes farther, so it takes longer" are both wrong. The sideways motion changes neither the time of the fall nor the vertical speed.
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