please help me with this question.

Dropa perpendicular from the top of the post to the particle position at the instant t seconds after the particle is launched. Take the oblique distance travelled to be 10t. Consequently, the toot of perpendiculaar dropped on the particle path from the top of post will be extended downwards to meet the ground at a point which will be its shadow. Calculate the distance of this point from the foot of lamp post in terms of t. Now the shadow has reached here in t seconds, So, speed of shadow = ditance travelled by shadow in t seconds/ time taken(t seconds). For the acceleration, extend the same approach with the speed in place of distance.

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