Question

9. An body is projected vertically upwards with
a velocity 'u' returns to the starting point in
4 seconds. The value of 'u' is (g = 10 m/s?]
Dla​

Answer 1

Answer:

20 m/s

Explanation:

Let the time taken to reach the highest point be t. And, at highest point velocity becomes 0.

But,

Time taken to reach = time taken to go down again

So,

Total time = t + t

= > 4 sec = 2t

= > 2 sec = t

Using equations of motions :

= > v = u + at

= > 0 = u + at

= > - u = at { a = - g }

= > - u = - gt

= > u = gt

= > u = (10)2

= > u = 20

Answer 2

Answer:

20 m/s

Explanation:

Let the time taken to reach the highest point be t. And, at highest point velocity becomes 0.

But,

Time taken to reach = time taken to go down again

So,

Total time = t + t

= > 4 sec = 2t

= > 2 sec = t

Using equations of motions :

= > v = u + at

= > 0 = u + at

= > - u = at { a = - g }

= > - u = - gt

= > u = gt

= > u = (10)2

= > u = 20

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