Space Time & Motion A.2 Forces & Momentum (id: fe2592b42)

本题目来源于试卷: Space Time & Motion A.2 Forces & Momentum，类别为 IB物理学

[单选题]
An apple falls 5 m in height from a tree. It re0zx a bky05.wjbou,rzgg*8:)vbs+g6tib ekgs+ o: p1gjwnds from the ground with a quarter of its striking spe1w v :ziorggb sbpgekgt+s)g ,:8+j6* ed. The apple is in contact with the ground for approximately 0.1
s. What is an estimate of the magnitude of the average net force on the apple when it strikes the ground?

A. $10^0$N
B. $10^1$N
C. $10^2$N
D. $10^3$N


参考答案:  B


本题详细解析:

$\underline{\text{Explanation}}$: 
Speed of the ball $v$ just before the hit;

$mgh=\frac{1}{2}m{v}^2$

$v=\sqrt{2gh}$

$v\approx 10m{s}^{-1}$

The magnitude of velocity just after the bounce back;

$v=2.5m{s}^{-1}$

The estimated mass of an apple is 0.1 kg.

Change in momentum;

$\mathrm{\Delta }p=p_2-p_1$

$=(-m{\displaystyle \frac{v}{4}})-mv$

$=-m{\displaystyle \frac{5v}{4}}$

$=(-0.1kg)({\displaystyle \frac{(5)(2.5)}{4}})m{s}^{-1}$

$=-1.25\approx 1.0\times 10^{0}kgm{s}^{-1}$

Duration of the collision is 0.1 s.

Force;

$F={\displaystyle \frac{\text{Change in Momentum}}{\text{Time}}}={\displaystyle \frac{1.0\times 10^{0}kgm{s}^{-1}}{1s}}=1.0\times 10^1$ N

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