A body of mass 0.6kg is thrown vertically upward... | WAEC SSCE - Physics - 2000 (Essay)

Question 1 Report

A body of mass 0.6kg is thrown vertically upward from the ground with a speed of 20ms\(^{-2}\). Calculate its;

(i) potential energy at the maximum height reached.

(ii) kinetic energy just before it hits the ground.

Answer

A body of mass \(m = 0.6\,\text{kg}\) is thrown vertically upward from the ground with initial speed \(u = 20\,\text{ms}^{-1}\).

(i) Potential energy at maximum height

By conservation of energy, at the highest point all the initial kinetic energy has become potential energy (the body is momentarily at rest):

\[ \text{P.E.}_{max} = \frac{1}{2}mu^{2} = \frac{1}{2}(0.6)(20)^{2} = \frac{1}{2}(0.6)(400) = 120\,\text{J} \]

(ii) Kinetic energy just before it hits the ground

Neglecting air resistance, the body returns to the ground with the same speed it left, so its kinetic energy just before impact equals its initial kinetic energy (equal also to the P.E. at the top):

\[ \text{K.E.} = \frac{1}{2}mu^{2} = 120\,\text{J} \]

Read lesson note on Newton’s Laws Of Motion (WAEC)

Read lesson note on Work, Energy And Power (WAEC)

Answer Details

A body of mass \(m = 0.6\,\text{kg}\) is thrown vertically upward from the ground with initial speed \(u = 20\,\text{ms}^{-1}\).

(i) Potential energy at maximum height

By conservation of energy, at the highest point all the initial kinetic energy has become potential energy (the body is momentarily at rest):

\[ \text{P.E.}_{max} = \frac{1}{2}mu^{2} = \frac{1}{2}(0.6)(20)^{2} = \frac{1}{2}(0.6)(400) = 120\,\text{J} \]

(ii) Kinetic energy just before it hits the ground

Neglecting air resistance, the body returns to the ground with the same speed it left, so its kinetic energy just before impact equals its initial kinetic energy (equal also to the P.E. at the top):

\[ \text{K.E.} = \frac{1}{2}mu^{2} = 120\,\text{J} \]

Read lesson note on Newton’s Laws Of Motion (WAEC)

Read lesson note on Work, Energy And Power (WAEC)

Newton’s Laws Of Motion

Work, Energy And Power

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A body of mass 0.6kg is thrown vertically upward from the ground with a speed of 20ms\(^{-2}\). Calculate its; (i) potential energy at the maximum height re...

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A body of mass 0.6kg is thrown vertically upward from the ground with a speed of 20ms\(^{-2}\). Calculate its; (i) potential energy at the maximum height re...

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