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# Kinetic Energy watch

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1. A particle of mass 5kg is moving at 2ms^-1 when it is acted on by a force of magnitude 10N for 2 seconds, causing it to accelerate. Find the increase in kinetic energy.

Thanks.
2. Before:

KE=1/2 mv^2

=5/2 x 4
=10J

After:

F=ma
10=5a
a=2
v=u+at
v=2+4
v=6

KE= 5/2 x 36
=90J

Change in KE=90-10=80J

Increase = 30J
3. (Original post by DOJO)
A particle of mass 5kg is moving at 2ms^-1 when it is acted on by a force of magnitude 10N for 2 seconds, causing it to accelerate. Find the increase in kinetic energy.

Thanks.
Initial KE = (1/2)(5)(2)^2 = 20/2 = 10 J

When acted on by force:
-> F = ma
-> 10 = 5a
-> a = 2 ms^-2

Hence: a = 2, t = 2, u = 2.
-> v = u + at = 2 + (2 * 2) = 4 + 2 = 6 ms^-1

Final KE = (1/2)(5)(6)^2 = 90 J

Increase in KE = Final KE - Initial KE = 90 - 10 = 80 J
4. (Original post by Nima)
Initial KE = (1/2)(5)(2)^2 = 20/2 = 10 J

When acted on by force:
-> F = ma
-> 10 = 5a
-> a = 2 ms^-2

Hence: a = 2, t = 2, u = 2.
-> v = u + at = 2 + (2 * 2) = 4 + 2 = 6 ms^-1

Final KE = (1/2)(5)(6)^2 = 90 J

Increase in KE = Final KE - Initial KE = 90 - 10 = 80 J
Cheers,

I would give both of you a postive rep but unfortunantly this thing is not
letting me!
5. (Original post by Nima)
When it lets you rep, give it to me, because the 1st poster was wrong in his/her answer.
Harsh Its not been a good day for me, I keep making silly mistakes, but give Nima the rep

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