# Homework Help: Find the initial acceleration of block B

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1. Dec 6, 2017

### Vivek098

1. The problem statement, all variables and given/known data
a block B of negligible mass is connected to a particle of mass 1 kg with a non-stretchable string. Now the hanging particle is given a velocity root(8gH) horizontally when system is at rest. Find the initial acceleration of block B.

2. Relevant equations
3. The attempt at a solution

Since Mass of Block is negligible, so Tension in String is Zero. Now for Block A, only force acting is mg in downward direction. So, acceleration of Block A is g in downward direction always. In the initial state, the acceleration of block A is equal to acceleration to Block B since they are directly connected by string. So, acceleration of Block B should be g towards right. But actual answer given is 2g.

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2. Dec 6, 2017

### PeroK

Try drawing a diagram of the situation after a short time. Hint: where are the two blocks?

3. Dec 6, 2017

4. Dec 6, 2017

### PeroK

You need a diagram after the particle has moved somewhat!

Hint: assume the experiment is taking place on the horizontal. I.e. ignore the vertical force of gravity. What do you get then?

PS The answer of $2g$ looks wrong to me.

5. Dec 6, 2017

### Vivek098

The acceleration is zero since there are no forces.

6. Dec 6, 2017

### PeroK

Are you sure? That means the block won't move?

7. Dec 6, 2017

### Abhishek kumar

How could be system initially at rest as mentioned in question. How block b will hold the tension produce in string by 1 kg block?

8. Dec 6, 2017

### PeroK

The 1kg block must be held in place by some external force: it perhaps ought to have been shown at the edge of a small supporting platform.

9. Dec 6, 2017

### Abhishek kumar

May be

10. Dec 6, 2017

### haruspex

Agreed. Should more than double that.
Or just instantaneously at rest, the two blocks having previously been propelled leftwards and upwards respectively.

11. Dec 6, 2017

### PeroK

Slightly trickier for a lab technician to arrange!