Work Energy And Power Question 242
Question: A steel ball of mass 5g is thrown downward with velocity 10 m/s from height 19.5 m. It penetrates sand by 50 cm. The change in mechanical energy will be
Options:
A) 1 J
B) 1.25 J
C) 1.5 J
D) 1.75 J
Show Answer
Answer:
Correct Answer: B
Solution:
[b] $ {v^{2}}=u^{2}+2gh ={{( 10 )}^{2}}+2\times 10\times 19.5 =490 $
K.E. at the ground $ =\frac{1}{2}mv^{2}=\frac{1}{2}\times \frac{5}{1000}\times 490=\frac{49}{40}J $
$ P.E=mgh=\frac{5}{1000}\times 10\times ( \frac{-50}{100} )=-\frac{1}{40}J $
$ \therefore $ Change in energy $ =\frac{49}{40}-( -\frac{1}{40} ) $
$ =\frac{50}{40}=1.25J $
