Hard
Question
A small ball rolls of the top of a stairway horizontally with a velocity of 4.5 m s-1. Each step is 0.2 m high and 0.3 m wide. If g is 10 ms-2, then the ball will strike the nth step where n is equal to (assume ball strike at the edge of the step).
Options
A.9
B.10
C.11
D.12
Solution
we have the point of projection as (0, 0)
we have the equation of st. line (as shown in fig.)
y = tanθ / x
y =
× ....(1)
Also the equation of trajectory for horizontal projection
y =
g 
....(2)
from (1) and (2)
or X =
=
= 3 × 0.9
If no. of steps be n then n × 0.3 = 3 × 0.9
n = 9
we have the equation of st. line (as shown in fig.)
y = tanθ / x
y =
× ....(1)Also the equation of trajectory for horizontal projection
y =
g ....(2)from (1) and (2)
or X =
=
= 3 × 0.9If no. of steps be n then n × 0.3 = 3 × 0.9
n = 9
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