Question

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Answer 1

Answer:

(b) 35

Explanation:

Given :

• Height risen to by the ball = u²/2g = 80 metres

• Time taken = t = 7 seconds

• Gravitational force = a = - 10 m/s²

To find:

• Displacement after 7 seconds

Maximum height = 80

u²/20=80

u²=1600

u = 40 m/s

Upward motion :

Final velocity = v = 0 m/s

Initial velocity = u = 40 m/s

Displacement = s = 80 metres

Acceleration = a = - 10 m/s²

Using second equation of motion :

S=ut+½×at²

80=40×t+½×-10×t²

80=40t-5t²

-5t²+40t-80=0

By solving :

t = 4 seconds

Downward motion:

Initial velocity = u = 0 m/s

Acceleration = a = 10 m/s²

Time = t = 7-4 = 3 seconds

Using the second equation of motion :

S=ut+½×at²

S=0×3+½×10×9

S=45 metres

Displacement = highest point - 45

Displacement = 80-45

Displacement = 35 metres

(b) 35 metres is correct

Answer 2

Explanation:

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