Answer:
The capacitance per unit length is 
(b) is correct option.
Explanation:
Given that,
Radius a= 2.50 mm
Radius b=7.50 mm
Dielectric constant = 3.68
Potential difference = 120 V
We need to calculate charge per length for the capacitance
Using formula of charge per length

Put the value into the formula


We know that,

We need to calculate the capacitance per unit length
Using formula of capacitance per unit length



Hence, The capacitance per unit length is 
Answer:
Initial velocity = 10 m/s
θ = 60°
This is the case of projectile motion
So the horizontal component of velocity 10 m/s = 10 cosθ
u = 10 cosθ
u = 10 cos 60°
u=5 m/s
x= 5 m
So in the horizontal direction
x = u .t
5 = 5 .t
t = 1 sec The vertical component of velocity 10 m/s = 10 sinθ
Vo= 10 sinθ
Vo= 10 sin 60°
Vo = 8.66 m/s
h=3.75 m
So height of robot = 3.75 - 0.75 m
height of robot =3 m
Thermometer there's others you can use but i know that's one of them