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๐ Revise, Reflect, Refine, Q15 (Page 138)
A coconut of mass 1.5 kg falls from the top of a coconut tree onto the wet sand on a beach. The height of the tree is 10 m. On impact, the coconut comes to rest by making a depression in the sand. (i) Calculate the velocity of the coconut just before it hits the sand. (ii) Assume that the average resistive force of sand is 3000 N and all of the coconut's energy is used to create the depression in the sand. Calculate the depth of the depression the coconut makes in the sand. Assume g = 10 m sโป².View answer
Answer- (i) Velocity of the coconut just before it hits the sand
Position Potential energy Kinetic energy Total mechanical energy Top of tree (10 m) 1.5 × 10 × 10 = 150 J 0 J 150 J Just before sand 0 J 150 J 150 J - ½mv² = 150
- v = √(2gh) = √(2 × 10 × 10) = √200
- v ≈ 14.1 m sโป¹
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(ii) Depth of the depression
- Energy of the coconut = 150 J
- This energy = work done against the sand's resistive force
- 150 = 3000 × d
- d = 150 / 3000
- d = 0.05 m = 5 cm
Q15 - A coconut of mass 1.5
Last updated at September 16, 2026 by Teachoo
