Question

Franklin lifts a 2kg weight vertically. If he lifts it so that way the velocity of the weight is constant, how much force is he using?

g=−9.8ms2

Possible Answers:

98N

39.2N

9.8N

4.9N

19.6N

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Answer 1

Correct answer:

19.6N

Explanation:

If the object has a constant velocity, that means that the net acceleration must be zero.

a=v2−v1t

v1=v2→a=0t=0

In conjunction with Newton's second law, we can see that the net force is also zero. If there is no net acceleration, then there is no net force.

Fnet=manet=m(0ms2)=0N

Since Franklin is lifting the weight vertically, that means there will be two force acting upon the weight: his lifting force and gravity. The net force will be equal to the sum of the forces acting on the weight.

Fnet=Flift+Fgravity

Since we just proved that the net force will equal zero, we can say −Fgravity=Flift.

We know the mass of the weight and we know the acceleration, so we can solve for the lifting force.

−Fgravity=Flift

−(mg)=Flift

−(−9.8ms2∗2kg)=Flift

−(−19.6N)=Flift

19.6N=Flift