Question

A motor car moving with a uniform speed of $20 \mathrm {~m} / \mathrm { sec }$ comes to stop on the application of brakes after travelling a distance of 10 m Its acceleration is

• A. $20 \mathrm {~m} / \mathrm { sec } ^ { 2 }$
• B. $- 20 m / \mathrm { sec } ^ { 2 }$
• C. $- 40 m / \sec ^ { 2 }$
• D. $+ 2 m / \sec ^ { 2 }$

Answer 1

Answer: (B)

$- 20 m / \mathrm { sec } ^ { 2 }$

Answer 2

From $v ^ { 2 } = u ^ { 2 } + 2 a S$ ⇒ $0 = u ^ { 2 } + 2 a S$

⇒ $a = \frac { - u ^ { 2 } } { 2 S } = \frac { - ( 20 ) ^ { 2 } } { 2 \times 10 } = - 20 \mathrm {~m} / \mathrm { s } ^ { 2 }$