Work/ kinetic energy theory

  • Thread starter shawli
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  • #1
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Homework Statement



A 5.75 kg object passes through the origin at time t = 0 such that the x component of velocity is 5.00 m/s and its y component of velocity is -3.00m/s.

a) what is the kinetic energy of the object at this time?

b) at t = 2.00s, the particle is located at x = 8.50m and y = 5.00m. What constant force acted on the object during this time interval?

Homework Equations



Change in K = Kfinal - Kinitial
where K = 1/2 * m * v^2

W= force * displacement

The Attempt at a Solution



I got part a by finding the magnitude of the object's velocity then plugging my known values into the K = 0.5mv^2 equation. I got my answer to be K = 97.8J at t=0.

I'm a bit lost on what to do for part b though...
 

Answers and Replies

  • #2
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You can compute how far the object traveled in 2 seconds. You know its speed at time = 0. Does this information suggest any other equation you might use to compute the average acceleration?

Knowing the average acceleration, you can compute the constant force.
 
  • #3
PeterO
Homework Helper
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Homework Statement



A 5.75 kg object passes through the origin at time t = 0 such that the x component of velocity is 5.00 m/s and its y component of velocity is -3.00m/s.

a) what is the kinetic energy of the object at this time?

b) at t = 2.00s, the particle is located at x = 8.50m and y = 5.00m. What constant force acted on the object during this time interval?

Homework Equations



Change in K = Kfinal - Kinitial
where K = 1/2 * m * v^2

W= force * displacement

The Attempt at a Solution



I got part a by finding the magnitude of the object's velocity then plugging my known values into the K = 0.5mv^2 equation. I got my answer to be K = 97.8J at t=0.

I'm a bit lost on what to do for part b though...
If the velocity had been unchanged for the 2 seconds, the object will have moved 10.0 in the x direction, and -6 in the y direction.

Instead it ended up where they said.

Treat each dirction separately to find the acceleration in the x-direction and y-direction. COmbine them to find the overall acceleration.

F = ma should give the required force.
 
  • #4
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Thanks!
 

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