Question

Two blocks of masses 5 kg and 10 kg are connected by a massless spring. A force of 20 N acts on 10 kg mass as shown. At the instant, 5 kg mass has an acceleration of $0.4m{s}^{-2}$,the acceleration of 10 kg mass is

• A. $2.9m{s}^{-2}$
• B. $1.8m{s}^{-2}$
• C. $3.5m{s}^{-2}$
• D. $1m{s}^{-2}$

Answer 1

The correct option is B $1.8m{s}^{-2}$

let the spring force at that instant is $F_{sp}$
FBD of 5 kg
$F_{sp}=5a_1\dots \dots \dots \dots [\because F_{net}=ma]$
$=5\times 0.4=2N$
FBD of 10 kg
net force= 20-2=18 N
$18=10a_2\Rightarrow a_{2}1.8m{s}^{-2}$
$\therefore$ Acceleration of 10 kg mass at the instant given is $1.8m{s}^{-2}$