91Ó°ÊÓ

Gravitational potential: The gravitational potential energy is stored in the body due to virtue of its position.

The expression of gravitational energy is given as,

$E_p=mgh$ (1.1)

Here, m is the mass of the object, g is the acceleration due to gravity, h is the height the object is lifted up from the surface of Earth.

(a)

The work done by the bird on snake to rise it from ground to a branch is stored in snake as form of potential energy.

$W=m_{s}gh$

Here,is the mass of snake, g is the acceleration due to gravity$\left(9.8\text{m}/{\text{s}}^2\right)$, and h is the height of the branch.

Putting all known values,

$\begin{array}{rcl}W& =& \left(75\text{g}\right)×\left(9.8\text{m}/{\text{s}}^2\right)×\left(2.5\text{m}\right)\\ & =& \left(75\text{g}\right)×\left(\frac{1\text{kg}}{1000\text{g}}\right)×\left(9.8\text{m}/{\text{s}}^2\right)×\left(2.5\text{m}\right)\\ & ≈& 1.84\text{J}\end{array}$

Therefore, the required work done by the bird on the snake is 1.84 J.

(b)

The work done by the bird to rise its own center of mass from ground to branch is,

$W=m_{b}gh$

Here,$m_b$is the mass of snake$\left(m_b=350\text{g}\right)$, g is the acceleration due to gravity $\left(9.8\text{m}/{\text{s}}^2\right)$, and h is the height of the branch$\left(h=2.5\text{m}\right)$.

Putting all known values,

$\begin{array}{rcl}W& =& \left(\text{350 g}\right)×\left(9.8\text{m}/{\text{s}}^2\right)×\left(2.5\text{m}\right)\\ & =& \left(350\text{g}\right)×\left(\frac{1\text{kg}}{1000\text{g}}\right)×\left(9.8\text{m}/{\text{s}}^2\right)×\left(2.5\text{m}\right)\\ & ≈& 8.58\text{J}\end{array}$

Therefore, the work done by the bird to rise its own center of mass to branch is 8.58 J.