28J because mechanical energy is the sum of the potential energy and kinetic energy
Given :
Initial velocity , u = 0 m/s² .
To Find :
The acceleration of the cart.
Solution :
Since, acceleration is constant.
Using equation of motion :

Putting, t = 1 s and x = 4 m in above equation, we get :

Therefore, the acceleration of the cart is 8 m/s².
Since velocity is a speed and a direction, there are only two ways for you to accelerate: change your speed or change your direction—or change both. If you're not changing your speed and you're not changing your direction, then you simply cannot be accelerating—no matter how fast you're going.
Let volume of empty boat be = 100% = 1V
and mass of boat be M
In water 10%, 0.1V of the volume is submerged.
Mass, m of 1200kg increases the submerging from 10%, 0.1V to 70%, 0.7V
M leads to 0.1V boat submerging
boat submerging.
M + 1200kg leads to 0.7V boat submerging.
This is 60%, 0.6 V increase
By comparison
(M+1200kg) * 0.1V = 0.7V * M
0.1M + 120kg = 0.7M
120kg = 0.7M - 0.1M
120kg = 0.6M
M = (120/0.6)kg
M = 200kg.
The mass of the boat is 200kg.
To solve this problem we will use the concepts related to Torque as a function of the Force in proportion to the radius to which it is applied. In turn, we will use the concepts of energy expressed as Work, and which is described as the Torque's rate of change in proportion to angular displacement:

Where,
F = Force
r = Radius
Replacing we have that,



The moment of inertia is given by 2.5kg of the weight in hand by the distance squared to the joint of the body of 24 cm, therefore


Finally, angular acceleration is a result of the expression of torque by inertia, therefore



PART B)
The work done is equivalent to the torque applied by the distance traveled by 60 °° in radians
, therefore


