MCQ
A ball of mass 100 g is projected with velocity $20 m / s$ at $60^{\circ}$ with horizontal. The decrease in kinetic energy of the ball during the motion from point of projection to highest point is :
- A20 J
- ✓15 J
- Czero
- D5 J
✓
Answer
Correct option: B.
15 J
(B) 15 J
Sol.
$\begin{array}{l} k _{ i }=\frac{1}{2} mv^2 \\ k _{ f }=\frac{1}{2} m\left( v \cos 60^{\circ}\right)^2=\frac{1}{8} mv ^2 \\ \Delta k = k _{ i }- k _{ f }=\frac{3}{8} mv ^2=\frac{3}{8} \times 0.1 \times 400=15 J\end{array}$
Sol.
$\begin{array}{l} k _{ i }=\frac{1}{2} mv^2 \\ k _{ f }=\frac{1}{2} m\left( v \cos 60^{\circ}\right)^2=\frac{1}{8} mv ^2 \\ \Delta k = k _{ i }- k _{ f }=\frac{3}{8} mv ^2=\frac{3}{8} \times 0.1 \times 400=15 J\end{array}$
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