91影视

• Mass of the man = 75 kg.
• Velocity = 30.0 m/s.
• Time = 2.00 s.

Calculate the acceleration as:

Apply the following equation of motion as:

$\mathit{\text{v}}\mathit{=}\mathit{\text{u}}\mathit{+}\mathit{\text{at}}$

Here, v is the final velocity, u is the initial velocity, a is the acceleration, and t is the time.

Substitute 30 m/s for v, 0 m/s for u, and 2 s for t in the above expression, and we get,

$\begin{array}{c}30\text{鈥刴/蝉}=0+a脳2s\\ a=\frac{30\text{鈥刴/蝉}}{2\text{鈥剆}}\\ a=15{\text{鈥刴/蝉}}^{\text{2}}\end{array}$

Determine the force exerted as:

Apply Newton鈥檚 Second Law of Motion as:

$F鈭�mg=ma$

Here, Fis the force, mis the mass of man, and gis the acceleration due to gravity.

Substitute 15 m/s² for a, 9.8 m/s² for g, and 75 kg for min the above expression, and we get,

$\begin{array}{c}F鈭�75\text{鈥刱驳}脳{\text{9.8鈥刴/蝉}}^2=75\text{鈥刱驳}脳15{\text{鈥刴/蝉}}^2\\ F鈭�735\text{鈥刱驳}鈰�{\text{m/s}}^2=1125\text{鈥刱驳}鈰�{\text{m/s}}^2\\ F=\left(1125+735\right)\text{鈥凬}\\ \text{F}=1860\text{鈥凬}\end{array}$

Calculate the ratio of force to weight as:

$\begin{array}{c}\frac{F}{mg}=\frac{1860\text{鈥凬}}{75\text{鈥刱驳}脳{\text{9.8鈥刴/蝉}}^2}\\ =\frac{1860\text{鈥凬}}{735\text{鈥凬}}\\ =2.53\end{array}$

Hence, the force is 1860 N, and the ratio of force to weight is 2.53

The value of the force of 1860 N is very large as experienced in an elevator. Elevators are not built to be so uncomfortable. He will probably fall.

The unreasonable premise is that the acceleration of the elevator is much higher, and also, the velocity is very high for an elevator.