Kinetic energy (KE) Questions

Question

Hey

 

Can someone please help me with this questions. Also explain how they got to the answer. I've spent hours on it but still not getting it. Any help would be brilliant.

 

Kinetic energy (KE) is calculated using the expression:
K.E=1/2 mv^2

 

If the mass is increased by 4%, and the velocity reduced by 3%, determine the approximate change in kinetic energy (KE).

Answer 1

This is not as hard as you think.  Any increase in percentage simply gets added to 100%, or 1.  Any decrease is likewise subtracted.  So your new mass is 1+.04, or 1.04m.  (1.04 times the original mass.)  And the new velocity would then be 0.97v.

 

• KE_new=(1/2)(1.04m)(0.97v)²       Plug in your new numbers
• KE_new=(1/2)(1.04m)(.9409)v²     Remember to square the .97!
• KE_new=(1/2)(.978536)mv²
• KE change= KE_new/KE_original
• KE change=0.978536
• The new KE is 97.8536% of the original KE  (You could also say that the new KE is decreased by 2.1464%)