Which two of the following statements about inertia are true? 1. Inertia is the force that keeps a moving object in motion.
2. Inertia is the force that keeps a stationary object at rest.
3. Inertia is the natural tendency of a stationary object to resist motion.
4. Inertia is the natural tendency of a moving object to resist a change in its velocity.

One day, after pulling down your window shade, you notice that sunlight is passing through a pinhole in the shade and making a small patch of light on the far wall. you see that the patch of light seems to be a circular diffraction pattern. it appears that the central maximum is about 1 cm across and you estimate that the distance from the window shade to the wall is about 3 m. what is (a) the average wavelength of sunlight? (b) the diameter of the pinhole?