A block of \(1\) kg is released from a top of a smooth curve AB, and then it encounters a rough surface BC, coming to rest at C. The work done by friction is: (\(g=10\) m/s²)
           
1. \(25\) J
2. \(50\) J
3. \(-25\) J
4. \(-50\) J

The work done by all the forces (external and internal) on a system equals the change in:

A body of mass \(1\) kg is thrown upwards with a velocity \(20\) ms^-1. It momentarily comes to rest after attaining a height of \(18\) m. How much energy is lost due to air friction?
(Take \(g=10\) ms^-2)
1. \(20\) J
2. \(30\) J
3. \(40\) J
4. \(10\) J

In a ballistics demonstration, a police officer fires a bullet of mass \(50.0\) g with speed \(200\) m/s on soft plywood of thickness \(2.00\) cm. The bullet emerges with only \(\text{10%}\) of its initial kinetic energy. The emergent speed of the bullet is:
1. \(0\)
2. \(53.2\) m/s
3. \(63.2\) m/s
4. \(6.32\) m/s