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 xqog f-b7*rw 7heigq(tm5 :ccn85 o: ezw 4hoqnbt1l5x,exht from a tree. It rebounds from the ground with a quarter of its striking speed. The apple is in contact with 4te5 m 51b onqte,cnh8cq:(x xw zlo:5the 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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