(ei) a 150-kg box is pushed horizontally along the floor with a force of 650 n. if the coefficient of friction
between the box and the floor is 0.21, calculate its acceleration.

2.28 m/s²

Explanation:

Draw a free body diagram of the box.  There are four forces on the box:

Weight force mg pulling down.

Normal force Fn pushing up.

Applied force F pushing right.

Friction force Fn μ pushing left.

Sum the forces in the y direction.

∑F = ma

Fn − mg = 0

Fn = mg

Sum the forces in the x direction.

∑F = ma

F − Fn μ = ma

F − mg μ = ma

a = (F − mg μ) / m

a = (650 N − 150 kg × 9.8 m/s² × 0.21) / 150 kg

a = 2.28 m/s²

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.