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In the ruler-drop test, the ruler falls 19.6 cm before Kiran catches it.

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

In the ruler-drop test, the ruler falls $19.6$ cm before Kiran catches it. Use $t = \sqrt{\dfrac{2d}{g}}$ with $g = 9.8\ \text{m/s}^2$ . What is his reaction time in milliseconds?

Need a reminder? The key ideaShow

A reflex is a quick, automatic response. Its path, the reflex arc, is receptor, sensory neuron, relay neuron in the spinal cord, motor neuron, effector. The ruler-drop test gives a reaction time: $t = \sqrt{\dfrac{2d}{g}}$ , with $d$ in metres and $g = 9.8\ \text{m/s}^2$ .

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.

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← Meera touches a hot iron and pulls her hand away at once.A message from the hand goes through the spinal cord along 1.0 m of nerve in a reflex. →

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