Secondary 1 Science Physical Sciences Quiz

Secondary 1 Science Quiz - Physical Sciences

Answer Key

Section A: Multiple Choice

1. B) 4.0 J [1]
Working: Work done = Force × distance = 5 N × 0.8 m = 4.0 J

2. C) A ball rolling along the ground [1]
Explanation: Kinetic energy is the energy of motion. A rolling ball is in motion, while the other options describe stored (potential) energy.

3. A) 0 J [1]
Explanation: Work done = Force × distance moved in the direction of the force. Since the bag is stationary, the displacement is 0 m, so work done = 10 N × 0 m = 0 J. Holding an object stationary requires effort but does no mechanical work.

4. C) Thermal energy [1]
Explanation: When brakes are applied, friction between the brake pads and wheels converts the car's kinetic energy into thermal energy (heat).

5. A) The gravitational potential energy at the top [1]
Explanation: By the law of conservation of energy, on a frictionless slope, all gravitational potential energy at the top is converted to kinetic energy at the bottom.

Section B: Short Answer

6. The law of conservation of energy states that energy cannot be created or destroyed; it can only be converted from one form to another, or transferred from one object to another, but the total energy in a closed system remains constant. [2]
Marking: [1] for stating energy cannot be created or destroyed; [1] for stating it is converted/transferred and total energy remains constant.

7. Using conservation of energy:
GPE at top = KE at bottom
mgh = ½mv²
0.5 × 10 × 10 = 0.5 × 0.5 × v²
50 = 0.25v²
v² = 200
v = √200 = 14.1 m/s (or 14 m/s to 2 s.f.) [3]
Marking: [1] for correct equation setup; [1] for correct substitution; [1] for correct final answer.
Alternative: v² = u² + 2as = 0 + 2(10)(10) = 200, v = 14.1 m/s. Acceptable.

8.

• Gravitational potential energy is the energy stored in an object due to its position (height) above a reference level. Example: A book on a shelf. [1]
• Kinetic energy is the energy possessed by an object due to its motion. Example: A moving car. [1]
  Marking: [1] for correct distinction; [1] for valid examples.
  Note: Students may also describe elastic potential energy or other forms — accept any valid pair with clear distinction.

9.
(a) Work done by student = F × d = 50 N × 4 m = 200 J [1]

(b) Work done against friction = F_friction × d = 10 N × 4 m = 40 J [1]

(c) Net work done = Work by student − Work against friction = 200 − 40 = 160 J [1]
Alternative: Net work = Net force × distance = (50 − 10) × 4 = 160 J. Acceptable.

10. A pendulum eventually comes to rest because its mechanical energy (kinetic + gravitational potential) is gradually converted into thermal energy due to air resistance and friction at the pivot point [1]. The total energy is conserved, but the mechanical energy decreases as it is transferred to the surroundings as heat [1].
Marking: [1] for identifying energy conversion to thermal; [1] for linking to conservation of energy / energy transfer to surroundings.

Section C: Structured Response

11.
(a) GPE at A = mgh = 400 × 10 × 20 = 80,000 J (or 80 kJ) [2]
Marking: [1] for correct formula and substitution; [1] for correct answer with unit.

(b) KE at C = 80,000 J [1]
Explanation: By conservation of energy, all the gravitational potential energy at A is converted to kinetic energy at C (since C is at ground level, GPE = 0), assuming no energy losses [1].

(c) KE at C = ½mv²
80,000 = ½ × 400 × v²
80,000 = 200v²
v² = 400
v = 20 m/s [3]
Marking: [1] for correct equation; [1] for correct substitution; [1] for correct answer with unit.

12.
(a) Weight = mg = 60 × 10 = 600 N [1]

(b) Work done = F × d = 600 × 2.0 = 1,200 J [2]
Marking: [1] for using weight as the force; [1] for correct answer with unit.

(c) Power = Work / Time = 1,200 / 1.5 = 800 W [2]
Marking: [1] for correct formula; [1] for correct answer with unit.

(d) The thermal energy comes from the chemical energy in the weightlifter's muscles [1]. Not all chemical energy is converted to gravitational potential energy — some is inevitably converted to thermal energy due to metabolic processes and muscle inefficiency.

13.
(a) When the ball leaves the boy's foot, it has kinetic energy [1]. As it rolls along the ground, friction between the ball and the ground converts the kinetic energy into thermal energy (heat) until the ball comes to rest [1].

(b) The ball does not return to the boy's foot because the kinetic energy has been converted into thermal energy and transferred to the ground and the ball [1]. This energy conversion is not spontaneously reversible — the thermal energy does not spontaneously convert back into kinetic energy of the ball. The law of conservation of energy is not violated; the total energy remains the same, but it has been dispersed as heat [1].

14.
(a) Work done = mgh
Ali: W = 50 × 10 × 9 = 4,500 J [1]
Bala: W = 60 × 10 × 9 = 5,400 J [1]

(b) Power = Work / Time
Ali: P = 4,500 / 30 = 150 W [1]
Bala: P = 5,400 / 25 = 216 W [1]

(c) Bala develops more power [1]. This is because Bala does more work (greater mass) in a shorter time.
Marking note: Award the mark for identifying Bala with a valid reason.

15.
(a) Work done by applied force = F × d = 12 × 3 = 36 J [1]

(b) KE gained = ½mv² = ½ × 2 × 4² = ½ × 2 × 16 = 16 J [2]
Marking: [1] for correct formula; [1] for correct answer with unit.

(c) The work done by the applied force (36 J) is greater than the kinetic energy gained (16 J) because some of the work done is used to overcome friction between the block and the surface [1]. This work against friction is converted into thermal energy, so only the remaining energy (36 − 20 = 16 J) appears as kinetic energy of the block [1].
Marking note: Students may calculate the work against friction = 36 − 16 = 20 J. Accept any clear explanation that accounts for the energy difference via friction.

Section D: Application and Data Interpretation

16.
(a) Using conservation of energy (Total energy = GPE + KE = 200 J at all heights):

[3] — Award [1] for each correct pair of values (3 pairs needed for full marks). Deduct [1] for each incorrect row, minimum 0.

(b) The law of conservation of energy [1] — as the ball falls, gravitational potential energy is converted into kinetic energy, and the total mechanical energy remains constant (assuming no air resistance).

17.
(a) GPE = mgh = 0.4 × 10 × 1.5 = 6.0 J [2]
Marking: [1] for correct formula and substitution; [1] for correct answer with unit.

(b) GPE after bounce = mgh = 0.4 × 10 × 1.0 = 4.0 J
Energy lost = 6.0 − 4.0 = 2.0 J [2]
Marking: [1] for calculating GPE after bounce; [1] for correct energy lost with unit.

(c) The lost energy is converted into thermal energy (in the ball and the floor) and sound energy [1]. Accept any one valid form.

18.
(a) Gravitational potential energy of water → Kinetic energy of flowing water → Electrical energy (via turbines and generators) [1].
Marking: Award [1] for identifying the main conversion chain. Accept abbreviated answers.

(b) The electrical energy output is less than the initial gravitational potential energy because some energy is lost as thermal energy due to friction in the pipes and turbines, and some as sound energy [1]. By the law of conservation of energy, the total energy is conserved, but not all of it is converted into useful electrical energy [1].

(c) Any one of:

• Use smoother pipes to reduce friction
• Use more efficient turbines
• Reduce the length of the penstocks
• Lubricate the turbine bearings
  [1] — Accept any reasonable suggestion that reduces energy loss.

19.
(a) Minimum work done = mgh = 70 × 10 × 12 = 8,400 J [2]
Marking: [1] for correct formula and substitution; [1] for correct answer with unit.

(b) Minimum power = Work / Time = 8,400 / 8 = 1,050 W [2]
Marking: [1] for correct formula; [1] for correct answer with unit.

(c) The actual power output is greater because the athlete also does work to move her limbs (arms and legs) and overcome internal friction in her muscles and joints [1]. Additionally, the athlete may not take the most direct path, and some energy is converted to thermal energy in her body.
Marking note: Accept any valid reason that accounts for additional energy expenditure beyond the minimum mgh.

20.
(a) From the graph, at speed = 20 m/s, KE ≈ 400 kJ [1]
Marking note: Accept values between 380–420 kJ due to reading from a sketched graph.

(b) The graph shows that kinetic energy increases with the square of the speed (non-linear / quadratic relationship) [1]. As speed increases, KE increases rapidly (curved upward trend).

(c) When the speed doubles from 10 m/s to 20 m/s, the kinetic energy should increase by a factor of 4 (since KE ∝ v²) [1]. From the graph: at 10 m/s, KE ≈ 100 kJ; at 20 m/s, KE ≈ 400 kJ. Since 400 = 4 × 100, the prediction is verified [1].
Marking: [1] for stating the factor of 4 relationship; [1] for verifying with values from the graph.

END OF ANSWER KEY