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Ezra is occasionally asked to work the check-out line during his shifts at the Hy-Vee grocery store. During a recent lesson on Newton's
Laws, he re-lived a memory from work. He wrote the following Physics problem and he wants you to solve it.
The handle of a paper grocery sack has a breaking strength of 298 N. Ezra loads the bag with 18.8-kg of soup cans. With what
maximum acceleration can he lift the sack upward without breaking the handles?

Respuesta :

Answer:

Approximately [tex]6.04\; {\rm m\cdot s^{-2}}[/tex], assuming that [tex]g = 9.81\; {\rm N \cdot kg^{-1}}[/tex] and that the mass of the bag is negligible.

Explanation:

There are two forces on the paper bag:

  • Upward tension in the handle, [tex]F(\text{tensions})[/tex], and
  • Downward weight of the bag and its contents, [tex]F(\text{weight})[/tex].

It is given that the tension in the handle [tex]F(\text{tension})[/tex] should not exceed [tex]298\; {\rm N}[/tex].

Let [tex]g[/tex] denote the gravitational field strength. The mass of the bag and its contents is [tex]m = 18.8\; {\rm kg}[/tex]. Their weight will be [tex]F(\text{weight})= m\, g[/tex].

SInce [tex]F(\text{tension})[/tex] and [tex]F(\text{weight})[/tex] are in opposite directions, the resultant force on the bag will be:

[tex]F(\text{net}) = F(\text{tension}) - F(\text{weight})[/tex].

Divide the net force by mass to find the acceleration [tex]a[/tex] of the bag:

[tex]\begin{aligned}a &= \frac{F(\text{net})}{m} \\ &= \frac{F(\text{tension}) - F(\text{weight})}{m} \\ &= \frac{F(\text{tension}) - m\, g}{m} \\ &= \frac{F(\text{tension})}{m} - g\end{aligned}[/tex].

Since [tex]F(\text{tension}) \le 298\; {\rm N}[/tex]:

[tex]\begin{aligned} a &= \frac{F(\text{tension})}{m} - g \\ &\le \frac{298\; {\rm N}}{18.8\; {\rm kg}} - 9.81\; {\rm N \cdot kg^{-1}} \\ &\approx 6.04\; {\rm N \cdot kg^{-1}} \\ &=6.04\; {\rm m\cdot s^{-2}}\end{aligned}[/tex].

Note the unit conversion: [tex]1\; {\rm N \cdot kg^{-1}} = 1\; {\rm (kg \cdot m\cdot s^{-2})\, kg^{-1}} = 1\; {\rm m\cdot s^{-2}}[/tex].

Answer:

Acceleration = 6.05 m/s²

Explanation:

Fmax = 298 N

m = 18.8 kg

g = 9.8 m/s²

___________

a - ?

According to Newton's 2nd law:

Fmax = m·(g + a)

g + a = Fmax / m

Acceleration:

a = Fmax / m - g

a = 298 / 18.8 - 9.8 ≈ 6.05 m/s²