Conservation of Energy — Homi Bhabha Class 9 Physics MCQs with Solutions
Free Homi Bhabha Class 9 Physics Conservation of Energy MCQs with step-by-step solutions (12 questions). Part of Work, Energy & Power. Practise online on Prepizo — no login needed.
▶ Practise Conservation of Energy online (free)
Questions with solutions
Q1 — Conservation of Energy · medium · theory
The law of conservation of energy states that energy:
A. can be created but not destroyed
B. is lost during every change
C. can neither be created nor destroyed, only changed from one form to another ✓ Correct
D. can be destroyed but not created
Solution: The total energy of an isolated system stays constant; it only transforms between forms.
Q2 — Conservation of Energy · hard · theory
For a freely falling body, as it falls its potential energy decreases and its kinetic energy:
A. remains constant
B. becomes zero
C. increases by the same amount ✓ Correct
D. decreases
Solution: P.E. converts to K.E. so that their sum (total mechanical energy) stays constant.
Q3 — Conservation of Energy · hard · numerical
A stone of mass 1 kg is thrown up and reaches a height of 8 m. Its potential energy at the top (taking $g = 10$ m/s²) equals its initial kinetic energy of:
A. 8 J
B. 800 J
C. 80 J ✓ Correct
D. 40 J
Solution: At the top all K.E. becomes P.E.: initial K.E. $= mgh = 1 \times 10 \times 8 = 80$ J.
Q4 — Conservation of Energy · medium · theory
In a simple pendulum swinging back and forth, the energy continuously changes between:
A. sound and kinetic
B. heat and light
C. kinetic and potential energy ✓ Correct
D. chemical and potential
Solution: At the extremes energy is potential; at the mean position it is kinetic — the two interchange.
Q5 — Conservation of Energy · hard · theory
A body falls from a height. At the mid-point of its fall (ignoring air resistance):
A. it has only kinetic energy
B. its total energy is halved
C. it has only potential energy
D. its kinetic energy equals its potential energy ✓ Correct
Solution: At half the height, half the initial P.E. has become K.E., so K.E. = P.E. there (total energy unchanged).
Q6 — Conservation of Energy · medium · theory
When a ball is dropped and bounces to a lower height each time, the "lost" mechanical energy is mainly converted into:
A. nuclear energy
B. chemical energy
C. heat and sound ✓ Correct
D. light and electricity
Solution: Energy is not destroyed; it is dissipated as heat and sound during each bounce.
Q7 — Conservation of Energy · medium · theory
In a hydroelectric power plant, the energy of falling water is converted mainly into:
A. electrical energy ✓ Correct
B. nuclear energy
C. chemical energy
D. sound energy
Solution: The potential/kinetic energy of falling water spins turbines and generators to produce electrical energy.
Q8 — Conservation of Energy · easy · theory
According to the law of conservation of energy, energy can...
A. Be destroyed but not created
B. Keep increasing on its own
C. Be created but not destroyed
D. Neither be created nor destroyed, only change from one form to another ✓ Correct
Solution: Energy can only be transformed from one form into another. The total amount of energy in an isolated system stays constant.
Q9 — Conservation of Energy · easy · theory
As a ball falls freely toward the ground, its...
A. Kinetic and potential energy both decrease
B. Potential energy decreases and kinetic energy increases ✓ Correct
C. Kinetic and potential energy both stay the same
D. Potential energy increases and kinetic energy decreases
Solution: As the ball falls its height decreases, so its potential energy decreases, while its speed increases, so its kinetic energy increases. The total stays constant.
Q10 — Conservation of Energy · medium · numerical
A ball of mass 1 kg is dropped from a height of 10 m. Ignoring air resistance and taking g = 10 m/s squared, its speed just before hitting the ground is about...
A. 10 m/s
B. 14 m/s ✓ Correct
C. 20 m/s
D. 100 m/s
Solution: All the potential energy converts to kinetic energy, so v = square root of (2 × g × h) = square root of (2 × 10 × 10) = square root of 200, which is about 14 m/s.
Q11 — Conservation of Energy · medium · theory
A ball is thrown straight up into the air. At the highest point of its path...
A. Its potential energy is maximum and its kinetic energy is momentarily zero ✓ Correct
B. Its kinetic energy is maximum and its potential energy is zero
C. Both its kinetic and potential energy are zero
D. Both its kinetic and potential energy are maximum
Solution: At the top the ball stops for an instant, so its kinetic energy is momentarily zero, while its height, and therefore its potential energy, is maximum.
Q12 — Conservation of Energy · hard · numerical
A pendulum bob of mass 0.2 kg is released from a point 0.45 m above its lowest position. Taking g = 10 m/s squared, its speed at the lowest point is...
A. 4.5 m/s
B. 9 m/s
C. 1.5 m/s
D. 3 m/s ✓ Correct
Solution: The potential energy at release becomes kinetic energy at the bottom: v = square root of (2 × g × h) = square root of (2 × 10 × 0.45) = square root of 9 = 3 m/s. The mass cancels out.