Question

(ii) a 20 kg ball is thrown upward with a speed of 4 m/s. (a) Find its potential
energy when it is it reaches the highest point.
(b) calculate the maximum height it reaches.
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Answer 1

S O L U T I O N :

Given,

• Mass (m) = 20 kg

• Initial velocity (u) = 4 m/s

• Final velocity (v) = 0 m/s [At the maximum height the velocity is zero]

• Acceleration due to gravity (g) = 9.8 m/s²

To Find,

• The maximum height it reaches.
• Find its potential energy when it is it reaches the highest point.

Explanation,

Case (I), The maximum height it reaches.

Applying 3rd equation of motion,

v² = u² - 2gH

[ Put the values ]

=> 0² = 4² - 2 × (9.8) × H

=> 0 = 16 - 19.6 × H

=> 19.6H = 16

=> H = 0.8 m

Case (II), Find its potential energy when it is it reaches the highest point.

Applying potential energy formula,

P.E = mgh

[ Put the values ]

=> P.E = 20 × 9.8 × 0.8

=> P.E = 196 × 0.8

=> P.E = 156.8 J