A crowbar 1.5 m long rests on a stone 0.25 m from the end under a 900 N load…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A crowbar long rests on a stone from the end under a load.
- What effort, at right angles to the bar at its other end, balances the load?
- What is the mechanical advantage?
Need a reminder? The key ideaShow
A rigid body is in equilibrium when the net force is zero and the net torque about every point is zero. Take torques about a point where an unknown force acts, so that it drops out.
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.
Plan. The stone is the pivot.
Step 1. (a) , so .
Step 2. (b) .
Answer: (a) . (b) .
Check. The arms are in the ratio , the same as the forces the other way round.
Watch out. The effort's moment arm is , not the bar's whole length.
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