(a) 1.01 cm
First of all, we need to find the spring constant of the spring.
The force initially applied to the spring is equal to the weight of the block hanging on it:
where m = 4.32 kg is the mass of the block and g = 9.8 m/s^2 is the acceleration of gravity.
When this force is applied, the spring stretches by
We can find the spring constant by using Hooke's law:
where k is the spring constant. Solving for k,
Later, the first object is removed and another object of mass
m' = 1.50 kg
is hung on the spring. The weight of this object is
So, if we use Hooke's law again, we can find the new stretching of the spring:
(b) 1.16 J
The work that must be done on the spring is equal to the elastic potential energy that would be stored in the spring, therefore:
where we have
k = 1448.6 N/m is the spring constant
x = 4.00 cm = 0.04 m is the new stretching
Solving the equation, we find the work that must be done by the external force:
Answer: The gravitational acceleration on planet X is 5 N/kg
On Earth (with the gravitational accelartion g_E) the mass of 2kg will correspond to
On planet X we are told the same measure is only 10N. Since there is a proportional relationship between g and F, we can calculate g_X: