Question:

A girl standing on a stationary lift (open from above) throws a ball upwards with initial speed $50 \,m \,s^{-1}$. The time taken by the ball to return to her hands is (Take $g= 10 \,m \,s^{-2}$)

Updated On: Jul 5, 2022
  • $5\,s$
  • $10\,s$
  • $15\,s$
  • $20\,s$
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The Correct Option is B

Solution and Explanation

Using, $S=ut+\frac{1}{2} at^{2}$ Here $S = 0$, $u = 50\,m\,s^{-1}$, $a=-g=-10\,m\,s^{-2}$ $\therefore 0=50t+\frac{1}{2}\times\left(-10\right)t^{2}=50t-5t^{2}$ $\Rightarrow t=10\,s$
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Notes on Motion in a straight line

Concepts Used:

Motion in a straight line

The motion in a straight line is an object changes its position with respect to its surroundings with time, then it is called in motion. It is a change in the position of an object over time. It is nothing but linear motion. 

Types of Linear Motion:

Linear motion is also known as the Rectilinear Motion which are of two types:

  1. Uniform linear motion with constant velocity or zero acceleration: If a body travels in a straight line by covering an equal amount of distance in an equal interval of time then it is said to have uniform motion.
  2. Non-Uniform linear motion with variable velocity or non-zero acceleration: Not like the uniform acceleration, the body is said to have a non-uniform motion when the velocity of a body changes by unequal amounts in equal intervals of time. The rate of change of its velocity changes at different points of time during its movement.