Kinematics Test

Result

Kinematics Test - 9

Score
-
out of -
Rank
-
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TIME Taken - -

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Question 1
1 / -0

A ball is projected upwards from the top of a tower, with velocity 50 ms^-1, making an angle 30° with the horizontal. The height of the tower is 70 m. After how many seconds, from the instant of throwing, will the ball reach the ground?
(g = 10 ms^-²)

A
2 s

B
5 s

C
7 s

D
9 s

Solution

Initial velocity along y axis, u_y= 50 sin30°
a = -10 m/s²
Displacement along y axis = S_y
S_y = u_yt + 0.5×a×t²
-70 = (50 sin30°×t) + 0.5 × (-10) × t²
5t² - 25t - 70 = 0
Solving,
t = -2 or t = 7
So, after t = 7 s, the ball will reach the ground from the instant of throwing.