A block of mass m is kept on a rough plank which moves with a horizontal acceleration a. If the plank was at rest at `t=0`, and the block does not slide relative to the plank, find the work done by friction on the (a) block, (b) plane, (c) system, (block+plank) during time `t`.

Explanation

To solve the problem step-by-step, we will analyze each part of the question regarding the work done by friction on the block, the plank, and the system as a whole.

### Given:
- Mass of the block = \( m \)
- Acceleration of the plank = \( a \)
- Time = \( t \)

### Part (a): Work done by friction on the block
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