Question 17
A child on a sledge
slides down a hill with acceleration a. The hill makes an angle θ with
the horizontal.
The total mass of the
child and the sledge is m. The acceleration of free fall is g.
What is the friction
force F ?
A m(g cosθ – a)
B m(g cosθ + a)
C m(g sinθ – a)
D m(g sinθ + a)
Reference: Past Exam Paper – June 2015 Paper 11 Q12
Solution:
Answer:
C.
The resultant force is
down along the slope.
Resultant force = ma
The weight may be resolved
into 2 components: one along the slope and one perpendicular to the slope.
Component of weight along
the slope = mg sinθ
Resultant force =
Component of weight along slope – Friction force
ma = mg sinθ – F
F = mg sinθ – ma
F = m (g
sinθ – a)
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