Answer:

Explanation:
Let say the empty wagon has mass "M"
now by newton's II Law we will have

now it is given that empty wagon is pulled with acceleration 1.4 m/s/s
now we will have

now a child of mass three times the mass of wagon is sitting on the empty wagon
so here we have


so we have

Mechanical energy = potential energy + kinetic energy
The ball is on the ground so it has no potential energy. that's all i know.
No, the speed at which an object falls is not equal to the acceleration at which it falls.
Answer:
Option B
Explanation:
Speed is defined as how fast an object can cover a specific distance and in what time it covers. So it is measured as the ratio of distance covered to the time taken to cover that distance. While acceleration is the rate of change of velocity. Moreover, speed is a scalar quantity and acceleration is a vector quantity. So most of the times, the direction will play an important role in the varying values of speed and acceleration. Also, acceleration of an object will depend upon the force and mass of the object. Thus, speed and acceleration will not attain same value always.