MCQ : Work And Energy - 2 Class 9 Science MCQs & solutions - Free

Work done = Mgh
Work will be maximum when the change in height is maximum, thus when it is lifted vertically upward.

Potential energy is given by the formula PE = m × g × h

For the first body at height h: PE₁ = mgh
For the second body at height 1.5h: PE₂ = mgh × 1.5

So the ratio is PE₁ : PE₂ = mgh : 1.5mgh = 1 : 1.5 = 2 : 3

Answer: b) 2 : 3

• Energy at start will be = Potential Energy = mgh
• According to the law of conservation of energy, it's total energy will be the same at all points i.e. = mgh.

Answer: (b) W = F.s

Work Done: The work done by a force is calculated as the product of the force and the displacement in the direction of the force.

Newton-metre is the unit of work.

Work is defined as the product of the force applied to an object and the distance it moves in the direction of that force. Here are some key points:

• The formula for work is: Work = Force × Distance.
• The unit of work is the joule, which is equivalent to one newton metre (1 J = 1 Nm).
• Work is done when a force causes an object to move; if there is no movement, no work is done.
• For example, if a force of 1 newton moves an object 1 metre, the work done is 1 joule.

In summary, the newton-metre is a measure of work, indicating how much energy is transferred when a force moves an object.

Answer:  0

The work done is zero when the force acting on a body causes no displacement.

Answer: (d) Kinetic Energy

Explanation: Kinetic energy is defined as the work needed to accelerate a body of a given mass from rest.

Answer: (a) Mechanical energy

Explanation: Mechanical energy = kinetic energy + potential energy

Answer: (d) All the above options

Explanation: Factors affecting kinetic energy are mass, momentum, and velocity.

They will have the same acceleration due to gravity because it is independent of mass. 

- Kinetic energy is given by the formula  KE = 1/2 mv²
- When two bodies are identical, they have the same mass.
- The kinetic energy depends on the square of the velocity.
- A higher velocity results in a higher K.E. 
- Therefore, the body with a higher velocity has higher kinetic energy.
- Correct answer: B: Higher Kinetic Energy.

• Since the free-falling acceleration is not dependent on mass, the final velocities of both masses are the same.
  The kinetic energy = KE = mv²/2
• Hence, the kinetic energy of the heavier mass will be more.

Answer: (c) 0

Explanation: If the displacement is perpendicular to the force, then the work done is zero.

• Work done by any force is the product of the component of the force in the direction of displacement and the magnitude of displacement.
  W = F.d = Fd cosθ
• When  W =−ve, it means cosθ = −ve
  Therefore, θ = 180º