Question

An object of mass 20kg is raised to a height of 10 m above the ground. What is its potential energy?
If the object is allowed to fall, find its kinetic energy when it is half way down.
g=10m/s​

Answer 1

GIVEN :-

• Mass of object ( m ) = 20 kg.
• Height ( h ) = 10 m.
• Acceleration due to gravity ( g ) = 10 m/s².

TO FIND :-

• The potential energy ( P.E ).
• The kinetic energy ( K.E ).

SOLUTION :-

As we know that,

$\implies \sf \: P.E_1 = mgh$

$\implies \sf \: P.E_1 =20 \: kg \times 10 \: m \times 10 \: ms ^{ - 2}$

$\implies \sf \: P.E_1 =2000 \: kg.m ^{2} .s ^{ - 2}$

As we know that , 1 kg.m²/s² = 1 J

$\implies \underline{ \boxed{\sf \: P.E_1 =2000 \: j}}$

Now According to question,

$\implies \sf \: P.E_2 = \dfrac{P.E_1}{2}$

$\implies \sf \: P.E_2 = \dfrac{2000 \: j}{2}$

$\implies \sf \: P.E_2 =1000 \: j$

Now,

$\implies \sf \: P.E_2 =K.E$

$\implies \underline{ \boxed{ \sf \: K.E = 1000 \: j}}$

Answer 2

$\Large{\underbrace{\underline{\bf{TO\: FIND\::}}}}$

1. Potential energy of object.
2. Kinetic energy of the object when it is half way down.

$\Large{\underbrace{\underline{\bf{GIVEN\::}}}}$

• Mass of an object is 20 kg.

• The object is raised to a height of 10 m above the ground.

$\Large{\underbrace{\underline{\bf{SOLUTION\::}}}}$

☛ To calculate the potential energy, we use the following formula.

$\orange\bigstar\:{\bf{\pink{P.E\:=\:m\:g\:h}}}\:\green\bigstar$

Where,

• m is the mass of the object.

• g is the gravitational acceleration = 10 m/s²

• h is the height raised by object.

➵ P.E = 20 × 10 × 10

➵ P.E = 2000 Joules

∴ Potential energy of the object is 2000 J.

✰ As we know that when object fall's from a height, then the potential energy of the object is converted into kinetic energy.

☛ Thus when object is at half way then kinetic energy of the object is,

➵ K.E = $\rm{\dfrac{Potential\: energy}{2}}$

➵ K.E = $\rm{\dfrac{2000}{2}}$

➵ K.E = 1000 Joules

∴ The kinetic energy of the object when it is half way down is 1000 J.