Răspuns:
a)
[tex]ec = \frac{m {v}^{2} }{2} [/tex]
Ec = 1800J
[tex]v = \sqrt{ \frac{ec}{ \frac{1}{2}m } } [/tex]
[tex]v = \sqrt{ \frac{1800j}{ \frac{1kg}{2} } } [/tex]
[tex]v = \sqrt{3600} = 60 \frac{m}{s} [/tex]
b) 4 kJ = 4000 J
m = 2×Ec/v^2 = 8000 J/ 100 m/s = 80 kg
