Answer: The most likely identity of the substance is iron.
Explanation:
The quantity of heat required to raise the temperature of a substance by one degree Celsius is called the specific heat capacity.

Q = Heat absorbed=
Joules
m= mass of substance = 11.9 g
c = specific heat capacity = ?
Initial temperature of the water =
= 25.0°C
Final temperature of the water =
= 45.0°CChange in temperature ,
Putting in the values, we get:


The specific heat of 0.45 is for iron and thus the substance is iron.
Answer:
(a). The spring compressed is
.
(b). The acceleration is 1.5 g.
Explanation:
Given that,
Acceleration = a
mass = m
spring constant = k
(a). We need to calculate the spring compressed
Using balance equation

....(I)
The spring compressed is
.
(b). If the compression is 2.5 times larger than it is when the mass sits in a still elevator,
The compression is given by

Here, acceleration is zero
So, 
We need to calculate the acceleration
Put the value of x in equation (I)




Hence, (a). The spring compressed is
.
(b). The acceleration is 1.5 g.
Thick lens will have shorter and consequently thin lens will have greater focal length. Because, For a thick lens, the optical path length of the light is more, than for a thin lens, thus, the bending of light will be more in case of a thicker lens. Consequently, it has a shorter focal length.
Given that,
Time = 0.5 s
Acceleration = 10 m/s²
(I). We need to calculate the speed of apple
Using equation of motion

Where, v = speed
u = initial speed
a = acceleration
t = time
Put the value into the formula


(III). We need to calculate the height of the branch of the tree from the ground
Using equation of motion

Put the value into the formula


(II). We need to calculate the average velocity during 0.5 sec
Using formula of average velocity


Where,
= final position
= initial position
Put the value into the formula


Hence, (I). The speed of apple is 5 m/s.
(II). The average velocity during 0.5 sec is 2.5 m/s
(III). The height of the branch of the tree from the ground is 1.25 m.