work and energy

example for thermal energy

Answer explanation

Thermal energy refers to the energy associated with heat. In this example, the correct choice is 'heat'.

kE +PE=

Answer explanation

The equation kE + PE= represents the conservation of mechanical energy.

Formula of PE

Answer explanation

PE stands for potential energy, which is calculated using the formula mgh, where m is the mass, g is the acceleration due to gravity, and h is the height. Therefore, the correct formula for PE is mgh.

Formula of KE

Answer explanation

The formula for kinetic energy (KE) is 1/2mv^2. The correct answer is 1/2mv^2.

When a body falls freely towards the earth, then its total energy

• (a) increases

• (b) decreases

• (c) remains constant

• (d) first increases and then decreases

Answer explanation

When a body falls freely towards the earth, its total energy remains constant. (c)

A car is accelerated on a levelled road and attains a velocity 4 times of its initial velocity. In this process the potential energy of the car

• (a) does not change

• (b) becomes twice to that of initial

• (c) becomes 4 times that of initial

• (d) becomes 16 times that of initial

Answer explanation

The potential energy of the car does not change as it is not affected by its velocity.

In case of negative work the angle between the force and displacement is

Answer explanation

In case of negative work, the angle between the force and displacement is 180 degrees, which is option (d).

An iron sphere of mass 10 kg has the same diameter as an aluminium sphere of mass is 3.5 kg. Both spheres are dropped simultaneously from a tower. When they are 10 m above the ground, they have the same

• (a) acceleration

• (b) momenta

• (c) potential energy

• (d) kinetic energy

Answer explanation

Both spheres experience the same acceleration due to gravity, regardless of their masses. Therefore, the correct choice is (a) acceleration.

A girl is carrying a school bag of 3 kg mass on her back and moves 200 m on a levelled road. The work done against the gravitational force will be (g =10 m s–2)

• 0.6 J

• zero

Answer explanation

The work done against the gravitational force is zero because the displacement is horizontal and perpendicular to the force.

Which one of the following is not the unit of energy?

• (a) joule

• (b) newton metre

• (c) kilowatt

• (d) kilowatt hour

Answer explanation

The unit of energy that is not mentioned in the answer choices is kilowatt.