A bodybuilder configures a leg-press apparatus (see figure) to a resistance of 1

Question

A bodybuilder configures a leg-press apparatus (see figure) to a resistance of 1050 N (about 236 lb). She pushes the weight to her full extension and comes to rest.

(a)What is the normal force on each of her feet?

(b) Assume she is able to move the push-plate of the leg-press machine at an acceleration of

0.50 m/s2 for the first half of the displacement. What is the normal force on each foot during this period of acceleration? Assume the resistive force is due to a mass with weight of 1050 N hanging on the cable of the leg-press apparatus.

The answer I found on this site is incorrect according to WebAssign.net.

I know part A is 525 N, I just can't figure out part B.

Explanation / Answer

a) in this case , since there is no acceleration , the 1050N weight is balanced by her foot,
hence normal reaction on each of her feet is,

N=(1050 N)/2

525 N
b)
the F be the force applied by the girl on the push plates.
normal reaction on her feet will be equal to F
in this case , F- 1050 = m*0.5
where m = 248 lbs
= 107.048 kg
F= 1050+107.048*0.5
= 1106.73544 N

therefore, the normal force on each feet is,

N=(1106.73544 N)/2

= 553.36 N

=553 N

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