Alex is asked to move two boxes of books in contact with each other and resting on a frictionless floor. he decides to move them at the same time by pushing on box a with a horizontal pushing force f p = 7.7 n. here box a has a mass ma = 12.1 kg and box b has a mass mb = 7.0 kg. the contact force between the two boxes is f c and n denotes the normal force.

2.8 N

Explanation:

Fp = 7.7 N

mA = 12.1 kg

mB = 7 kg

Let a be the acceleration and Fc be the contact force between A and B.

By the free body diagram, use Newton's second law

Fp - Fc = mA x a ..... (1)

Fc = mB x a ..... (2)

Adding both the equations

Fp = (mA + mB) x a

7.7 = (12.1 + 7) x a

a = 0.4 m/s^2

Substitute this value in equation (2), we get

Fc = 7 x 0.4 = 2.8 N

Thus, the contact force between the two blocks is 2.8 N.

Explanation:

the correct answer is D.