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Friction can hold a heavy crate with up to 240 N…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Friction can hold a heavy crate with up to . Once it slides, friction is . Four people push in turn with , , and .
- Find the friction force each time.
- Find the net force each time.
- What does the crate do?
Need a reminder? The key ideaShow
Friction acts between surfaces that touch, against sliding. It matches a push up to a limit; once the object slides, friction is usually a little less than that limit.
The net force adds all the forces with their directions. If it is zero the forces are balanced and the motion does not change; if not, they are unbalanced and the object speeds up, slows down or turns. Forces at right angles are added separately.
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. Pushes of , and . Up to the limit: friction matches each push, the net force is , and the crate stays put.
Step 2. The push. Over the limit, so the crate slides and friction is .
Step 3. Net force. , so the crate speeds up.
Answer: Friction , , , ; net force , , , ; only the last push moves it.
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