An object in space is initially stationary relative to the Earth. Then, a force

Question

An object in space is initially stationary relative to the Earth. Then, a force begins acting
on the object, starting with a force of 0 N, and
increasing at a uniform rate until the magnitude of the force is 40 N after the force has
acted for 20 s. The body has a mass of 15 kg.
What is the speed of the object at 20 s?

1. 2.66667 m/s
2. Insu?cient information to answer
3. 1.33333 m/s
4. 26.6667 m/s
5. 1066.67 m/s
6. 1777.78 m/s
7. 3555.56 m/s
8. 533.333 m/s
9. 53.3333 m/s

Explanation / Answer

since force increasing at a uniform rate let F=kt at t=20 , F=40 => k =2 =>F=2t => a = 2t/15 dv/dt = 2t/15 => v = t^2/15 => at t=20 v= 400/15= 26.66 m/s^2 hence 4 is the option

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