Question

A body of mass 2kg is thrown vertically upwards with a initial velocity of 20m/s. What will be it's potential energy at the end of 2 s. ( Assume g = 10 m/s^2.)

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Answer 1

According to question we have given,

Mass (m) = 2 kg

acceleration due to gravity (g) = - 10 m/s²

[Because body is thrown vertically upward due to this g is negative and g = a]

Initial velocity (u) = 20 m/s

Time (t) = 2 sec

Now,

Formula applied here is;

s = ut + $\dfrac{1}{2}$ at² (It is 2nd equation of motion)

s = 20 × 2 + $\dfrac{1}{2}$ × (-10) × (2)²

s = 40 - $\dfrac{1}{2}$ (10) × 4

s = 40 - 5 × 4

s = 40 - 20

$\textbf{s = 20 m}$

Now, we have to find it's kinetic energy at the end of the ground.

But during reaching the ground it's kinetic energy convert into potential energy.

So, that means we have to find it's potential energy.

[acceleration of gravity towards earth/ground always positive]

So, g = + 10

Potential energy = mgh

$\textbf{Potential energy}$ = 2 × 10 × 20

= $\textbf{400 J}$