ANSWER:
250 J
STEP-BY-STEP EXPLANATION:
F = 20N is required to stretch the spring by 4 meters
We know that the force is equal to:

We solve for k (spring constant):

The work done in stretching the spring is given by the following equation (in this case the stretch is 10 meters:

The work required is 250 joules.
The intaneuos velocity of an object is the
Gold cyanidation, aka MacArthur-Forrest process.
Answer:
(a) 
(b) 
Explanation:
Let:
mass of father be, 
mass of son be, 
speed of son be, 
initial speed of father be, 
After speeding up, speed of father is 
<u>We know Kinetic Energy is given as</u>
.....................................(1)
where:
m = mass
v = velocity
Hence, according to the initial condition the father is having kinetic energy half the kinetic energy of the son.



.................................................(2)
According to the final condition:



.....................................................(3)
(a)
From eq. 2 & 3





(b)
<em>putting the above value in eq. (2)</em>
