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Quiz Chapter 7: Energy and Power

10 questions · Form 3 Science Bab 7: Energy and Power

Question 1 of 10Score: 0

A $1 kg$ rock is dropped from rest from a height of $20 m$. What is its kinetic energy right before it hits the ground? (Ignore air resistance, $g = 10 m s-2$)

Full Question List & Answer Key

Prefer reading to quizzing? All 10 questions are listed below with the answer and explanation under each one.

1. A $1 kg$ rock is dropped from rest from a height of $20 m$. What is its kinetic energy right before it hits the ground? (Ignore air resistance, $g = 10 m s-2$)

  1. 20 J
  2. 100 J
  3. 200 J
  4. 400 J
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Answer: C

Gain in Kinetic Energy = Loss in Gravitational Potential Energy = $mgh = 1 × 10 × 20 = 200 J$.

2. Using conservation of energy, calculate the velocity of a $0.5 kg$ ball dropped from a height of $5 m$ just before hitting the floor ($g = 10 m s-2$).

  1. $10 m s-1$
  2. $25 m s-1$
  3. $50 m s-1$
  4. $100 m s-1$
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Answer: A

$mgh = 12 m v2 arrow v = √2gh = √(2 × 10 × 5) = √100 = 10 m s-1$.

3. A worker pushes a crate with a constant horizontal force of $50 N$ across a smooth floor over a distance of $4 m$. How much work is done by the worker?

  1. 12.5 J
  2. 54 J
  3. 200 J
  4. 20 J
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Answer: C

Work $W = F × s = 50 N × 4 m = 200 J$.

4. A student weighing $450 N$ climbs a staircase of vertical height $4 m$ in $6 seconds$. What is the useful power generated by the student?

  1. 1800 W
  2. 300 W
  3. 112.5 W
  4. 675 W
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Answer: B

Work $W = F × s = 450 N × 4 m = 1800 J$. Power $P = 18006 = 300 W$.

5. Why does a bouncing rubber ball eventually stop bouncing after being dropped from a height?

  1. Gravity gradually reduces the ball's total mass.
  2. Mechanical energy is gradually converted into heat and sound energy due to air friction and impact.
  3. Elastic energy inside the ball is completely destroyed.
  4. The Principle of Conservation of Energy stops applying after multiple impacts.
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Answer: B

Total energy is conserved, but mechanical kinetic/potential energy transforms into non-mechanical forms (heat, sound) during each impact and through air resistance.

6. A simple pendulum swings back and forth between points A, B, and C (where B is the lowest point). At which position is its kinetic energy at a MAXIMUM?

  1. At position A (highest left point)
  2. At position B (lowest central point)
  3. At position C (highest right point)
  4. At both A and C
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Answer: B

At the lowest position (B), gravitational potential energy is converted entirely into kinetic energy, reaching maximum speed.

7. What is the formula used to calculate the kinetic energy ($E_k$) of a moving object?

  1. $E_k = mgh$
  2. $E_k = 12 F x$
  3. $E_k = 12 m v2$
  4. $E_k = F × s$
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Answer: C

Kinetic energy of a mass $m$ moving at speed $v$ is given by $E_k = 12 m v2$.

8. In which of the following scenarios is NO work done according to physics definition?

  1. Lifting a $5 kg$ box from the floor onto a table
  2. Pushing a heavy concrete wall without moving it
  3. Pulling a toy car across the floor
  4. Climbing up a flight of stairs
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Answer: B

Work requires displacement in the direction of applied force ($W = F × s$). Since displacement is zero ($s = 0$), no work is done.

9. What happens to the potential energy of a roller coaster cart as it descends down a steep track slope?

  1. Potential energy increases and converts into elastic energy.
  2. Potential energy decreases and converts into kinetic energy.
  3. Potential energy remains constant while kinetic energy increases.
  4. Potential energy drops to zero immediately at the top of the slope.
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Answer: B

As height decreases, gravitational potential energy decreases while converting directly into kinetic energy (speeding up the coaster).

10. If the speed ($v$) of a moving vehicle is DOUBLED, how does its kinetic energy change?

  1. Doubles (2x)
  2. Triples (3x)
  3. Quadruples (4x)
  4. Remains unchanged
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Answer: C

Since $E_k \propto v2$, doubling the velocity increases kinetic energy by $(2)2 = 4$ times.

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