The slope of a position/time graph is the speed of the motion.
(The slope doesn't 'determine' the speed; it only displays it.)
The slope of a speed/time graph is the acceleration of the motion.
The speed of light in a material is given by:

where

is the speed of light in vacuum
n is the refractive index of the material
The lens in this problem has a refractive index of n=1.50, therefore the speed of light in the lens is

And the correct answer is C).
Rub a balloon on a woolen fabric to pick up some electrons, to make the balloon negatively charged, and stick them to a wall, which would be positively charged to make them stick.
Opposites attract and when you stick a negatively charged objects to positively charged objects, they tend to stick together. When you pick up electrons, it increases the number of electrons which will make the object negatively charged.
Note: The first part of the answer is a single sentence. The problem says in a complete sentence, so just in case that you need only one sentence you can take the first part. If you can add in more than a sentence, you can put in more from the second paragraph.
Answer:
(B) The total internal energy of the helium is 4888.6 Joules
(C) The total work done by the helium is 2959.25 Joules
(D) The final volume of the helium is 0.066 cubic meter
Explanation:
(B) ∆U = P(V2 - V1)
From ideal gas equation, PV = nRT
T1 = 21°C = 294K, V1 = 0.033m^3, n = 2moles, V2 = 2× 0.033=0.066m^3
P = nRT ÷ V = (2×8.314×294) ÷ 0.033 = 148140.4 Pascal
∆U = 148140.4(0.066 - 0.033) = 4888.6 Joules
(C) P2 = P1(V1÷V2)^1.4 =148140.4(0.033÷0.066)^1.4= 148140.4×0.379=56134.7 Pascal
Assuming a closed system
(C) Wc = (P1V1 - P2V2) ÷ 0.4 = (148140.4×0.033 - 56134.7×0.066) ÷ 0.4 = (4888.6 - 3704.9) ÷ 0.4 = 1183.7 ÷ 0.4 = 2959.25 Joules
(C) Final volume = 2×initial volume = 2×0.033= 0.066 cubic meter
It's downward vector from the centre of apple in the direction to the centre of the Earth.