Question

A body of mass 1 kg is taken from infinity to a point P. When the body reaches that point, it has a speed of 2 $m{s}^{-1}$. The work done by the conservative force is - 5 J. Which of the following is true (assuming non-conservating and pseudo-forces to be absent).

• A. Work done by the applied force is +7 J.
• B. The total energy possessed by the body at P is +7 J.
• C. The potential energy possessed by the body at P is +5 J.
• D. Work done by all forces together is equal to the change in kinetic energy.

Answer 1

Answer: (A), (C), (D)

Work done by the applied force is +7 J.
The potential energy possessed by the body at P is +5 J.
Work done by all forces together is equal to the change in kinetic energy.

$\Delta KE=$ Work done by all forces

$\Rightarrow \frac{1}{2}\left(1\right){\left(2\right)}^2=W+(-5)$

$\Rightarrow W=7$ Joule

Since there is no non-conservative forces acting on the body. So, the net work done must by the change in mechanical energy.

$KE+PE=W$

$2+PE=7$

$PE=5$ Joule