[填空题]
A projectile is launched a v8cv)d t gbe52ha+. fhe)x-dz:4rv sst an angle of6/y3yovdp 3xf $30^{\circ}$ to the horizontal with a speed of $ 30 \mathrm{~m} / \mathrm{s}$. How does the horizontal component of its velocity 1.0 s after launch compare with its horizontal component of velocity 2.0 s after launch?
参考答案: 26±2%
本题详细解析: The horizontal component of the velocity stays constant in projectile m; w.s/eay2 w+ja pwy8rotion, assuming that air resistance is negligible. Thus the horizontal component of velocity 1.0 seconds after launch will be the same as the horizontal component of 2 v/2a 8w;a. sw+rpeyjwyelocity 2.0 seconds after launch. In both cases the horizontal velocity will be given by $ v_{x}=v_{0} \cos \theta=(30 \mathrm{~m} / \mathrm{s})\left(\cos 30^{\circ}\right)=26 \mathrm{~m} / \mathrm{s} $.
