MC question!
A person who weights 800N steps onto a scale that is on the floor of an elevator car. If the elevator accelerates upward at a rate of 4.9m/s^2, what will the scale read?
A. 400N
B. 800N
C. 1000N
D. 1200N
E. 1600N
- Answer's D, but how?

Question

MC question! 
A person who weights 800N steps onto a scale that is on the floor of an elevator car. If the elevator accelerates upward at a rate of 4.9m/s^2, what will the scale read?
A. 400N
B. 800N
C. 1000N
D. 1200N
E. 1600N
- Answer's D, but how?

anonymous · Answer

|dw:1388579688985:dw|

loser66 · Answer

upward F = m(g+a)
downward F = m(g-a)

loser66 · Answer

when the elevator is at rest, F = mg --> m = F/g = 800/9.8 = 81.63kg
 so, upward F = 81.63 (9.8 +4.9)=1199.961 N = 1200N , it's D

anonymous · Answer

Got it @Loser66! Thanks :)