[单选题]
An apple falls 5 m in height from a tree. It rebounds fr02ibueqrp-w .38 t.+yopv;lxo )fkreom the ground ud,n av 8.ij6szj)w i3with a quarter of its striking speed. The apple is in contact wid6)a.8ju in3vizw , jsth 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:
Explanation: Speed of the ball v just before the hit;
mgh=21mv2
v=2gh
v≈10ms−1
The magnitude of velocity just after the bounce back;
v=2.5ms−1
The estimated mass of an apple is 0.1 kg.
Change in momentum;
Δp=p2−p1
=(−m4v)−mv
=−m45v
=(−0.1kg)(4(5)(2.5))ms−1
=−1.25≈1.0×100kgms−1
Duration of the collision is 0.1 s.
Force;
F=TimeChange in Momentum=1s1.0×100kgms−1=1.0×101 N