You are here
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 s⁻².
Show Answer
(i)
v
=
2gh
=
2 × 10 × 10
=
200
≈ 14.1
m s
-1
.
(ii) Energy at impact
= mgh
= 1.5 × 10 × 10
= 150
J
. This equals work done against the sand
= F × d
:
3000 × d
= 150
⇒ d
= 0.05
m
= 5
cm
.
= 2gh
= 2 × 10 × 10
= 14.1 m s -1
= 1.5 × 10 × 10
= 150 J
