# Reflex action

1. Jan 20, 2007

### ritwik06

arvind drops a scale vertically which is grabbed by Vijay whose hand is just below the scale. In the mean time the scale slips by 20cm. What is the reflex time of Vijay?

2. Jan 20, 2007

### cristo

Staff Emeritus
Do you know any equations that may help you here? (hint: constant acceleration).

Is there a reason why this is in the tutorial forum? In future please post in the homework forum.

3. Jan 20, 2007

### ritwik06

yes, the acceleration will be 9.8 m/sec^2. But how will this help?

oh! I am sorry once again. I havent understood till now, as to which question should I post in which section. I am sorry again.

4. Jan 20, 2007

### cristo

Staff Emeritus
Correct. Do you know any equations that will help you here? You are told the displacement, and you know that the initial velocity is zero.

That's ok. I'm sure it'll be moved for you soon anyway! In future though, use the homework forum. It's the second forum in the list on the front page (just under the tutorial forum)

5. Jan 20, 2007

### ritwik06

Nope which equation are you talking about?

Ok! I will use the homework section. Thanks!

sorry once again.

6. Jan 20, 2007

### cristo

Staff Emeritus
Have you come across the kinematic equations, for constant acceleration? Here's a link to them (scroll about half way down the page): kinematic equations. Which one do you think is most useful in this case?

7. Jan 20, 2007

### ritwik06

will the 3rd one help? I have not studdied kinematics yet :S

8. Jan 20, 2007

### cristo

Staff Emeritus
Ok, well you should use the first equation:$$d=v_it+\frac{1}{2}at^2$$. Here, note that vi=0, so this simplifies the equation somewhat. a is the acceleration due the gravity (9.81), d is the distance measured on the ruler, and t is the reaction time that you require.

Last edited: Jan 20, 2007