Question

A ball is thrown vertically upwards with a velocity of 20 m s^-1 from the top of a multistory building of 20 m high. How high will the ball rise? (Take g = 10 m s^-2)

• A. 10 m
• B. 15 m
• C. 20 m
• D. 25 m

Answer 1

Answer: (C)

20 m

Answer 2

Taking vertical upward motion of the ball upto highest point.

Here, $\mathrm { u } = 20 \mathrm {~ms} ^ { - 1 }$

V = 0 (At highest point velocity is zero)

$\mathrm { a } = - \mathrm { g } = - 10 \mathrm {~ms} ^ { - 2 }$

As $\mathrm { v } ^ { 2 } = \mathrm { u } ^ { 2 } + 2 \mathrm { as }$

$0 = ( 20 ) ^ { 2 } + 2 ( - 10 ) ( S )$

$S = \frac { 20 \times 20 } { 20 } = 20 \mathrm {~m}$