10. The elevator in the new office building warns that it can safely lift 300 kg at one time. If John (850N), Betty (530N), Robert (740N), and Alice (610N) all get in the elevator at once, can the elevator safely carry them up to the third floor?

I can't tell right away.  The elevator's limit is given in terms of mass, but the four people are listed in terms of their weights.  In order to compare them, we'll have to convert one or the other.

The total of the four people's weights is:

John . . . . . . . 850N

Betty . . . . . . . 530N

Robert . . . . . . 740N

Alice . . . . . . . .610N

Total . . . . . . 2,730N

The elevator can't accept more than 300 kg of mass.

The weight of any mass is (mass) x (gravity).

On Earth, 300kg weighs (300kg) x (9.8 m/s²) = 2,940 N.

Wonderful !  

2,730N is less than 2,940N.

Yes ! According to Otis' engineers, John, Betty, Robert and Alice can safely ride the elevator together, (although Betty and Alice may have a different opinion).

b would be the answer

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