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Sunday, January 5, 2020

An object of mass 0.30 kg is thrown vertically upwards from the ground with an initial velocity of 8.0 m s-1.


Question 39
An object of mass 0.30 kg is thrown vertically upwards from the ground with an initial velocity of 8.0 m s-1. The object reaches a maximum height of 1.9 m.

How much work is done against air resistance as the object rises to its maximum height?
A 4.0 J                         B 5.6 J                         C 9.6 J                        D 15 J





Reference: Past Exam Paper – June 2016 Paper 13 Q17





Solution:
Answer: A.


The object is thrown with an initial velocity of 8.0 m s-1. So, it has some initial kinetic energy.


At the object moves up, its kinetic energy is converted into gravitational potential energy. Some of the kinetic energy is expended as work done against air resistance.

KE at bottom = GPE at max height + Work done against air resistance


KE at bottom = ½ mv2 = ½ × 0.30 × 82 = 9.6 J


GPE at top = mgh = 0.30 × 9.8 × 1.9 = 5.586 J


KE at bottom = GPE at max height + Work done against air resistance
9.6 = 5.586 + Work done against air resistance

Work done against air resistance = 9.6 – 5.586 = 4.014 J

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