Q. 134.3( 25 Votes )

# An object of mass 40 kg is raised to a height of 5 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 = 10 m/s^{2})

Answer :

Given,

Mass, *m* = 40 kg

Acceleration due to gravity, *g* = 10 m/s^{2}

Height, *h* = 5 m

We know that,

Potential energy = *m* × *g* × *h*

= 40 × 10 × 5

= 2000 J

When the object is fall to its half way down, then its height above the ground =

=2.5 m

Now, Potential energy = *m* × *g* × *h*

= 40 × 10 × 2.55 J

= 1000 J

Now, we know that according to the law of conservation of energy:

Total potential energy = Potential energy at half way down + Kinetic energy at half way down

2000 = 1000 + Kinetic energy at half way down

Kinetic energy at half way down = 2000 – 1000

= 1000 J

Rate this question :

When a ball is thrown inside a mocking bus, does its kinetic energy depend on the speed of the bus? Explain.

Lakhmir Singh & Manjit Kaur - PhysicsA bullet of mass 15 g has a speed of 400 m/s. What is its kinetic energy? If the bullet strikes a thick target and is brought to rest in 2 cm, calculate the average net force acting on the bullet. What happens to the kinetic energy originally in the bullet?

Lakhmir Singh & Manjit Kaur - PhysicsA car is accelerated on a leveled road and attains a speed of 4 times its initial speed. In this process, the kinetic energy of the car:

A. Does not change

B. Becomes 4 times that of initial kinetic energy

C. Becomes 8 times that of initial kinetic energy

D. Becomes 16 times that of initial kinetic energy

Lakhmir Singh & Manjit Kaur - PhysicsCan any object have momentum even if its mechanical energy is zero? Explain.

NCERT Science - ExemplarWrite true or false for the following statements :

If we know the speed and mass of an object we can find out its kinetic energy.

Evergreen - ScienceWrite true or false for the following statements :

When velocity is halved, its kinetic energy becomes 1/4^{th}.

A 1 kg mass has a kinetic energy of 1 joule when its speed is:

Evergreen - ScienceWhen the speed of a moving object is doubled, its :

Evergreen - Science