Question

Match the physical situation on the left with the graph on the right. The graphs depict the variation of total energy ($E$), potential energy ($U$) and kinetic energy ($KE$) with time.

Answer 1

Concept used: Total mechanical Energy is conserved

if no external force is doing work on the system

(A) system : mass + spring + Earth

Motion : The mass will undergo simple

Harmonic motion.

At Extreme points : velocity = V=0

KE =0

$u=u_{max}=E$

Throughout the motion : $E=k+u=$ constant.

$Ans:2$

(B) system : Object + Earth

Motion : There is constant

acceleration so v will keep increasing $\Rightarrow K.E$ will increase

As Fext = O so E = K.E + u = const

-u = mgh as h is decreasing u will decrease.

$Ans:3$

(C) system : Object + Earth

Motion : $-Fext\ne 0\Rightarrow$ constant Acceleration $\Rightarrow$ v will increase $\Rightarrow$ K.E will increase

-u = mgh = constant as h = constant

- E = K.E + u $\Rightarrow$ E will increase

$Ans:1$

(D) system : Block + Earth

Motion : $\because V=$constant

$\therefore K.E=$ constant $(K.E=\frac{1}{2}m.v^2)$

$-u=mgh$, as h is decreasing $\Rightarrow u$ is decreasing

$-E=KE+u\Rightarrow E$ is decreasing

$Ans:4$