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Question

If a ball is thrown vertically upwards with the speed $u$, the distance covered during the second-to-last $t$ seconds of its ascent is
(Assume $t$ is less than half of the total ascent time).

The correct answer is
$\frac{3}{2}gt^2$

To solve this problem, we need to understand the motion of a ball thrown vertically upwards and the kinematics involved in its ascent.

Let's break down the problem:

  • The ball is thrown upwards with an initial velocity \(u\).
  • We need to find the distance covered during the second-to-last \(t\) seconds of its ascent.
  • Let \(T\) be the total time of ascent.

The time taken to reach the topmost point of its trajectory, where its velocity becomes zero, can be calculated using the formula:

\(T = \frac{u}{g}\)

where \(g\) is the acceleration due to gravity.

Now, we are interested in the second-to-last \(t\) seconds of the ascent.

The last \(t\) seconds of the ascent refers to the interval from \(T - t\) to \(T\).

The velocity of the ball at time \(T-t\) can be found using the equation:

\(v = u - g(T-t)\)

Simplifying, using \(T = \frac{u}{g}\), we get:

\(v = u - g \left( \frac{u}{g} - t \right) = gt\)

The velocity of the ball at \(t\) seconds before it reaches the peak is \(gt\).

Now, the distance covered in these \(t\) seconds can be calculated using the equation of motion:

\(s = vt - \frac{1}{2}gt^2\)

Substituting for \(v\) as \(gt\), we have:

\(s = gt \times t - \frac{1}{2}gt^2 = gt^2 - \frac{1}{2}gt^2\)

Simplifying, we get:

\(s = \frac{3}{2}gt^2\)

Thus, the distance covered during the second-to-last \(t\) seconds of its ascent is \(\frac{3}{2}gt^2\).

The correct option is:

$\frac{3}{2}gt^2$

.

 

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Important Questions from Acceleration due to gravity of the earth

  1. In an elevator, the actual weight of a person is equal to the apparent weight when:

  2. At what height above the surface of the earth does the weight of an object reduce by 1%. Given the radius of the earth is 6400.

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  4. The radii of two planets are respectively R 1and R 2and their densities are respectively ρ 1and ρ 2. The ratio of the acceleration due to gravity (g 1/g 2) at their surface is

  5. Let We and Wm be the weight of an object on the Earth and the Moon, respectively. Then, the ratio We/Wm is equal to _____.
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