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Question

A ball is thrown vertically upward with a speed of 30 m/s. The magnitude of its displacement after 4 s will be ______ (Take \(g = 10 \text{ m/s}^2\).)

This question was previously asked in
RRB ALP 2018 CBT 2 Fitter Question Paper (21-Jan-2019) (Shift 3)
The correct answer is
40 m

The problem asks for the magnitude of the displacement of a ball thrown vertically upward after a certain time.

Physics Displacement Calculation

We can use the kinematic equation for displacement under constant acceleration:

\( \Delta y = v_0 t + \frac{1}{2} a t^2 \)

Where:

  • \( \Delta y \) is the displacement.
  • \( v_0 \) is the initial velocity.
  • \( t \) is the time.
  • \( a \) is the acceleration.

Applying Values to the Formula

Given:

  • Initial velocity, \( v_0 = +30 \text{ m/s} \) (taking upward as positive).
  • Time, \( t = 4 \text{ s} \).
  • Acceleration due to gravity, \( a = -g = -10 \text{ m/s}^2 \) (acting downward).

Substitute these values into the equation:

\( \Delta y = (30 \text{ m/s})(4 \text{ s}) + \frac{1}{2} (-10 \text{ m/s}^2)(4 \text{ s})^2 \)

Step-by-Step Calculation

  1. Calculate the first term: \( v_0 t = 30 \times 4 = 120 \text{ m} \).
  2. Calculate the second term: \( \frac{1}{2} a t^2 = \frac{1}{2} (-10) (4)^2 = \frac{1}{2} (-10) (16) = -5 \times 16 = -80 \text{ m} \).
  3. Add the terms: \( \Delta y = 120 \text{ m} + (-80 \text{ m}) = 120 \text{ m} - 80 \text{ m} = 40 \text{ m} \).

The magnitude of the displacement after 4 seconds is 40 meters.

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Similar Questions

  1. A ball thrown up vertically returns to the ground after 10 second. Find the velocity with which it was thrown up? (if g = 10 m/s2).
  2. A body falling from rest has 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 _____ times '\(h\)' .
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Important Questions from Kinematic equations for uniformly accelerated motion

  1. Which of the following is an equation of motion?

    I. u = v + at

    II. 2as = v 2– u 2

  2. A ball is thrown vertically upward with a speed of 40 m/s. The time taken by the ball to reach the maximum height would be approximately
  3. A ball thrown up vertically returns to the ground after 10 second. Find the velocity with which it was thrown up? (if g = 10 m/s2).
  4. If the distance travelled by a body in the $n^{th}$ second is given by $(7 + 5n)$ m, then find the initial velocity and acceleration of the body respectively.

  5. Which of the following is an equation of motion?

    I. u = v + at

    II. 2as = v 2– u 2

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