[单选题]
An apple falls 5 m in height le3lc l2 b2qyp-l )*nfz 7a -byjh)4ekfrop9.yw+xkm jz,m a tree. It rebounds from the ground with a quarter of its striking speed. The apple is in ck,.z yp+ wmx9jontact 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. N
B. N
C. N
D. 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