The minimum force required just to move a block on a rough horizontal surface is `5N`. The block fails to move when a force of `3N` is applied on it. Static frition is .

Options

A. `5N`
B. `3N`
C. `4N`
D. `zero`

Answer

To find the static friction acting on the block, we can follow these steps:

### Step 1: Understand the Forces Acting on the Block
The block is on a rough horizontal surface and experiences two main forces: the applied force and the static friction force. The applied force is 3 N, and static friction acts in the opposite direction to prevent the block from moving.

### Step 2: Identify the Maximum Static Friction
The problem states that the minimum force required to move the block is 5 N. This means that the maximum static friction force (f_s_max) is also 5 N.

### Step 3: Analyze the Applied Force
When a force of 3 N is applied to the block, it does not move. This indicates that the static friction force is balancing this applied force. Since the block is not moving, the static friction force (f_s) must be equal to the applied force of 3 N.

### Step 4: Conclude the Value of Static Friction
Since the applied force is 3 N and the block does not move, the static friction force is also 3 N. This is less than the maximum static friction force of 5 N, which confirms that the block remains at rest.

### Final Answer
The static friction acting on the block when a force of 3 N is applied is **3 N**.

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