Current Electricity and Electrical InstrumentHard
Question
Two stones are thrown up simultaneously from the edge of a cliff 240 m high with initial speed of 10 m/s and 40 m/s respectively. Which of the following graph best represents the time variation of relative position of the second stone with respect to the first ? (Assume stones do not rebound after hitting the ground and neglect air resistance, take g = 10 m/s2) (The figure are schematic and not drawn to scale)
Options
A.
B.
C.
D.
Solution
For particle 1
- 240 = + 10t -
gt2
5t2 - 10t - 240 = 0
t1 = 8 sec
For particle 2
- 240 = 40t -
gt2
5t2 - 40t - 240 = 0
t2 = 12 sec
for 0 < t < 8 sec → arel = 0
straight line x-t graph
for 8 < t < 12 sec → arel = - g
downward parabola
for t > 12 sec → Both particles comes to rest
- 240 = + 10t -
gt25t2 - 10t - 240 = 0
t1 = 8 sec
For particle 2
- 240 = 40t -
gt25t2 - 40t - 240 = 0
t2 = 12 sec
for 0 < t < 8 sec → arel = 0
straight line x-t graph
for 8 < t < 12 sec → arel = - g
downward parabola
for t > 12 sec → Both particles comes to rest
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