Question

In a shotput event, an athlete throws the shotput of mass $10kg$ with an initial speed of $1m{s}^1$ at ${45}^{\circ }$ from a height $1.5m$ above ground. Assuming air resistance to be negligible and acceleration due to gravity to be $10m{s}^2$, the kinetic energy of the shotput when it just reaches the ground will be:

• A. $2.5J$
• B. $5.0J$
  
• C. $52.5J$
  
• D. $155.0J$
  

Answer 1

The correct option is D $155.0J$

Given,

$m=10kg$

$v=1m/s$

$h=1.5m$

$g=10m/s^2$

Change in mechanical energy is zero.

$\Delta (M.E)=0$

From the above figure,

$\Delta (K.E)+\Delta (P.E)=0$

$(K.E{)}_B-(K.E{)}_A+(P.E{)}_B-(P.E{)}_A=0$

$(K.E{)}_B-\frac{1}{2}m{v}^2+mg(0)-mgh=0$

$(K.E{)}_B=\frac{1}{2}m{v}^2+mgh$

$(K.E{)}_B=\frac{1}{2}\times 10\times 1\times +10\times 10\times 1.5$

$(K.E{)}_B=5+150$

$(K.E{)}_B=155.0J$

The correct option is D.