contestada

A 0.37 kg rock is thrown vertically upward from the top of a 37 m
cliff. When it hits the ground at the base of the cliff, the rock has a
speed of 33 m/s. Consider that air resistance is negligible. Use
conservation of total mechanical energy principle to find

a. The initial speed of the rock.
b. The greatest height of the rock as measured from the base of the
cliff.
c. Comment on the types of mechanical energy of the rock when
i) it is thrown upward, ii) it reached the maximum height, and
iii) it reached the base of the cliff.

Respuesta :

(a) The initial speed of the rock is 19.1 m/s.

(b) The greatest height of the rock as measured from the base of the

cliff is 55.6 m.

(c) i. As the ball is thrown up, its kinetic energy is converted to potential energy.

ii. When then ball reaches the maximum height, its kinetic energy becomes zero and it will have maximum potential energy.

iii. When the rock reaches the base of the cliff, its potential energy becomes zero and it will have maximum kinetic energy.

Conservation of mechanical energy

The initial speed of the rock is determined by applying the principle of conservation of mechanical energy as shown below;

Ui + K.Ei = Uf + K.Ef

mghi + ¹/₂mvi² = mghf + ¹/₂mvf²

(0.37 x 9.8 x 37) + ¹/₂(0.37)vi² = (0.37 x 9.8 x 0) + ¹/₂(0.37 x 33)²

134.16 + 0.185vi² = 0 + 201.47

0.185vi² = 201.47 - 134.16

0.185vi² =  67.31

vi² = 67.31/0.185

vi² = 363.84

vi = √363.84

vi = 19.1 m/s

Height reached by the rock from top cliff

vf² = vi² - 2gh

0 = vi² - 2gh

2gh = vi²

h = vi²/2g

h = (19.1)²/(2 x 9.8)

h = 18.6 m

Maximum height reached by rock from the base of the cliff

The maximum height from the base = 37 m + 18.6 m = 55.6 m

When the ball is thrown up, its kinetic energy is converted to potential energy.

When then ball reaches the maximum height, its kinetic energy becomes zero and it will have maximum potential energy.

When the rock reaches the base of the cliff, its potential energy becomes zero and it will have maximum kinetic energy.

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