Question 3

# A ball, thrown vertically upward, rises to a height of 80 m and returns to its original position. The magnitude of its displacement after 7 s of motion will be - (take g = 10 m/s$$^2$$)

Solution

A ball is thrown vertically upward , rises to a height of 80m.
at height of 80m, velocity of ball = 0
so, v² = u² + 2as
0 = u² + 2(-10)(80)
u = 40m/s
now, v = u + at
0 = 40 - 10t
t = 4sec
hence, time taken to reach 80m height = 4sec.
now, after that , ball falls vertical downward.
after 3 sec body reach h from the topmost point.
so, h = 1/2 gt² = 1/2 × 10 × 3² = 45m

hence, magnitude of total displacement = 80m + 45m = 125m

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