Homework Help: Physics kinetic energy

Posted by Aisumi on Saturday, October 30, 2010 at 2:17am.

Okay the equation for kinetic energy is = 1/2mv^2 so how would i figure this out??

If a semi-truck decreases its speed from 10 m/s to 5 m/s, its new Kinetic Energy is:

a)4 times its old Kinetic Energy
b)2 times its old Kinetic Energy
c)1/2 its old Kinetic Energy
d)1/4 its old Kinetic Energy
okay since the v is half of what it was would it be c????

Physics kinetic energy - Jordan, Saturday, October 30, 2010 at 10:05am
because v is the only thing changing the value of m is not relevant. to find out what would happen to the energy we compare the differences in v

ie 10^2 = 100
5^2 = 25
since the new v value is a quarter of the previous value the answer is (d)

alternatively, your reasoning before is correct but you have forgotten that the v value is squared ie 0.5^2 = 0.25

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