Question 24
A boy on a bicycle
starts from rest and rolls down a hill inclined at 30°to the horizontal.
The boy and bicycle
have a combined mass of 25 kg.
There is a frictional
force of 30 N, which is independent of the velocity of the bicycle.
What is the kinetic
energy of the boy and the bicycle after rolling 20 m down the slope?
A 1850 J B 2450 J C 3050 J D 3640 J
Reference: Past Exam Paper – June 2016 Paper 12 Q17
Solution:
Answer: A.
As the boy rolls down the
slope on his bicycle, the gravitational potential energy is converted into
kinetic energy (due to motion) and work done against friction.
GPE at top - - - > KE
at bottom + Work done against friction
The slope is inclined at
30° to the horizontal and the length of
the inclined slope of 20 m.
Vertical height of boy at
top of slope = 20 sin 30°
GPE at top = mgh = 25 × 9.81 × 20 sin 30°
Work done against friction
= F × d = 30 × 20 = 600 J
GPE at top = KE + Work
done against friction
25 × 9.81 × 20 sin 30° = KE + 600
KE = 1852.5 = 1850 J
No comments:
Post a Comment
If it's a past exam question, do not include links to the paper. Only the reference.
Comments will only be published after moderation