Two block of mass 4 kg and 2 kg are attached by an inextensible light string as shown in figure. Both the blocks are pulled vertically upwards by a force F=120N

Find
(a) the acceleration of the blocks,
(b) tension in the string. (Take g=`10 ms^(-2)`)

Options

A. 10, 40
B. 12, 40
C. 20, 40
D. 40, 35

Answer

A

Explanation

(a) Let a be the acceleration of the blocks and T the tension in the string as shown in figure.l

Taking the two blocks and the string as the system.
Using `sumF_(y)=ma_(y)` , we get
`F-4g-2g=(4+2)a`
or `120-40-20=6a" or " 60=6a`
`therefore a=10 ms^(-2)`
(b) Free body diagram of 2 kg blocks is shown below.

Using ` sum F_(x)=ma_(y)`
we get, T-2g=2a
or T-20=(2)(10)
`therefore T=40N`