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A block of mass 2 kg moving on a horizontal surface with speed of 4 ms –1 enters a rough surface ranging from x = 0.5 m to x = 1.5 m. The retarding force in this range of rough surface is related to distance by F = –kx where k = 12 Nm –1 . The speed of the block as it just crosses the rough surface will be :

1. Zero
2. 1.5 ms –1
3. 2.0 ms –1
4. 2.5 ms –1

Correct answer: 2.0 ms –1

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