Answer:
Gravitational lensing is how we know there is dark matter
What this means is that the light is bending as the light travels from the source to the observer, and if there are any 'holes' in between the beam, that is where 'dark matter' exists
Explanation:
Answer:
The hairs would have acquired charge by the passing of dry winds resulting in the loss of electron.
Explanation:
While standing on the top of a mountain if a person gets its hairs stand up after a cloud passes over, this might happen due to the static electric charges on the lower surface of the cloud are opposite in nature to that of hairs which the hairs would have acquired by the passing of dry winds which would have resulted in the loss of electron from the hair tip.
Similar case happens when we rub a dry plastic ruler or a dry plastic comb on our hairs.
Answer:
Question 1)
a) The speed of the drums is increased from 2 ft/s to 4 ft/s in 4 s. From the below kinematic equations the acceleration of the drums can be determined.

This is the linear acceleration of the drums. Since the tape does not slip on the drums, by the rule of rolling without slipping,

where α is the angular acceleration.
In order to continue this question, the radius of the drums should be given.
Let us denote the radius of the drums as R, the angular acceleration of drum B is
α = 0.5/R.
b) The distance travelled by the drums can be found by the following kinematics formula:

One revolution is equal to the circumference of the drum. So, total number of revolutions is

Question 2)
a) In a rocket propulsion question, the acceleration of the rocket can be found by the following formula:

b) 
PV = 400 x 0.08 = 32 J
Hope this helps