**Explanation:**

When an object is dropped from a height, it undergoes free fall. During free fall, the only force acting on the object is the force of gravity. As the object falls, its potential energy is converted into kinetic energy.

**Step 1: Calculate the potential energy at a height of 4 metres.**

The potential energy (PE) of an object at a certain height is given by the equation:

PE = mgh

where m is the mass of the object, g is the acceleration due to gravity, and h is the height.

Given:
m = 1 kg (mass of the stone)
g = 9.8 m/s² (acceleration due to gravity)
h = 4 m (height)

PE = (1 kg)(9.8 m/s²)(4 m) = 39.2 J

So, the potential energy of the stone at a height of 4 metres is 39.2 J.

**Step 2: Calculate the potential energy at a height of 1 metre.**

Using the same formula, we can calculate the potential energy at a height of 1 metre.

Given:
m = 1 kg (mass of the stone)
g = 9.8 m/s² (acceleration due to gravity)
h = 1 m (height)

PE = (1 kg)(9.8 m/s²)(1 m) = 9.8 J

So, the potential energy of the stone at a height of 1 metre is 9.8 J.

**Step 3: Calculate the kinetic energy at a height of 1 metre.**

The kinetic energy (KE) of an object is given by the equation:

KE = 0.5mv²

where m is the mass of the object and v is its velocity.

Since the stone is dropped from rest, its initial velocity is 0 m/s.

Given:
m = 1 kg (mass of the stone)
v = 0 m/s (initial velocity)

KE = 0.5(1 kg)(0 m/s)² = 0 J

So, the kinetic energy of the stone at a height of 1 metre is 0 J.

**Step 4: Calculate the total energy at a height of 1 metre.**

The total energy (TE) of an object is the sum of its potential energy and kinetic energy.

TE = PE + KE

TE = 9.8 J + 0 J = 9.8 J

So, the total energy of the stone at a height of 1 metre is 9.8 J.

Therefore, the correct answer is option B) 40 J.

There one formula for this here dx=4. means distance from ground so formula = mgdxso 1×10×4=40j.