Solve the following physics problems: 5. Calculate energy given power and time. 6. Explain why a sharp knife cuts better. 7. Analyze forces on an inclined plane. 8. Describe rotational equilibrium for

$$
E = 60 \text{ W} \times 1 \text{ s}
$$
$$
E = 60 \text{ J}
$$
A. $\boxed{\text{60 J}}$

6. A sharp knife cuts better because it has a smaller surface area at its edge. According to the formula $P = \frac{F}{A}$, a smaller area ($A$) for the same force ($F$) results in a greater pressure ($P$), allowing it to cut more effectively. B. has a smaller surface area, increasing pressure.

7. When a block rests on an inclined plane with an angle $\theta$, the component of its weight parallel to the plane is $W \sin \theta$, and the component perpendicular to the plane is $W \cos \theta$. As the angle of the incline increases:

   • $\sin \theta$ increases, so the parallel component ($W \sin \theta$) increases.
   • $\cos \theta$ decreases, so the perpendicular component ($W \cos \theta$) decreases. A. The component of weight parallel to the plane increases while the perpendicular component decreases.

8. For a seesaw (lever) to be perfectly balanced and not rotate, it must be in rotational equilibrium. This condition is met when the sum of all clockwise moments about the pivot is equal to the sum of all anticlockwise moments about the pivot. A. The total clockwise moment equals the total anticlockwise moment about the pivot.