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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. Which of the following statements about the mass of a body is correct?

  2. A body freely falling from rest has acquired a velocity ‘v’ after it falls through a distance ‘h’. The distance it has to fall down further for its velocity to become double is:

  3. On earth, the value of G = 6.67 × 10 -11  Nm 2kg -2 . What is the value on moon, where acceleration due to gravity is nearly one - sixth than that of earth?

  4. What is the force required to produce an acceleration of 9.8 m/s 2on a body of weight 9.8N? Take g = 9.8 m/s 2.

  5. 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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