I need help on this, it is to fill in these letters that that one word, when you see it you will understand about it but i really need help on all of this.

If a particle moves along a path such that r : (3 sin t) m and ? : 2t rad, where t is in seconds. what is the particle's acceleration in m/s in 4 seconds? a)- 16.43 b)- 16.29 c)- 15.21 d)- 13.79

What is the heat treatment of metals? what is the benefit of it? why and how it's useful? answer in details, do not write by hand.

The short distance from the objective lens to the object causes problems at high magnification. which of the following is the most serious? a. cleaning the object surface b. positioning the object c. reflection from the object surface. d. illumination of the object