Question

At two positions kinetic energy and potential energy of a particle are $K_1=10J:U_1=-20J,K_2=20J,U_2=-10J$
In moving from 1 to 2,

• A. work done by conservative force is positive
• B. work done by conservative force is negative
• C. work done by all forces is positive
• D. work done by all forces is negative

Answer 1

Answer: (B), (C)

The correct options are
B work done by conservative force is negative
C work done by all forces is positive

$\text{Step 1: Work done by conservative forces}$

Conservative forces are those forces whose work done does not depends on path.

$W_{cons}=U_i-U_f=(-20)-(-10)J$

$=-10J$

$\text{Step 2: Work done by all forces}$

From work-energy theorem, we can write

$W_{Net}=K_2-K_1$

$\Rightarrow W_{Net}=20-10=10J$

Hence, $B$ and $C$ are correct option.