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Home» class 9»Science» Chapter 9: Gravitation

A ball is thrown vertically upwards with a velocity of 49 m/s.... - Science

Question

A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate

(i) the maximum height to which it rises,

(ii) the total time it takes to return to the surface of the earth.

Answer

Given:

  • Initial velocity (u) = 49 \text{ m/s}

  • Final velocity at maximum height (v) = 0 \text{ m/s}

  • Acceleration due to gravity (g) = -9.8 \text{ m/s}^2 (upward motion)

(i) Maximum height (h):
Using the equation: v^2 - u^2 = 2gh
0^2 - (49)^2 = 2 \times (-9.8) \times h
-2401 = -19.6h
h = \frac{2401}{19.6}
h = 122.5 \text{ m}

(ii) Total time (t):
First, find the time to reach the top using: v = u + gt
0 = 49 + (-9.8)t
9.8t = 49
t = \frac{49}{9.8} = 5 \text{ s}

Total time = Time of ascent + Time of descent
Since time of ascent = time of descent:
Total time =5 + 5

Total time = 10 \text{ s}