W=Wđ​+Wt​=23​Wt​+Wt​=25​Wt​

\(\Rightarrow W = \frac{5}{2} . m g h\)

\(\Rightarrow m = \frac{2 W}{5 g h} = \frac{2.37 , 5}{5.10.3} = 0 , 5\) kg

Ta có: \(W_{đ} = \frac{3}{2} W_{t} \Rightarrow \frac{1}{2} m v^{2} = \frac{3}{2} m g h\)

\(\Rightarrow v = \sqrt{3 g h} = \sqrt{3.10.3} = 9 , 49\) m/s

tóm tắt

m = 2 tấn =2000 kg

v = 21,6 km/h = 6 m/s

t = 15 s

g = 10 m/s bình phương

a = \(\frac{v}{t}\) =\(\frac{15}{6}\) =0,4 m/s bình phương

a,

F = ma = 2000 \(\cdot\) 0,4 = 800 N

s = \(\frac12at^2\) = \(\frac12\cdot0,4\cdot15^2\) = 45 m

A = F . s = 800 . 45 = 36000 J

P = \(\frac{A}{t}\) =\(\frac{36000}{15}\) =2400W

b,\(\)

Fms = \(\mu mg\) = 0,5 . 2000 . 10 = 1000N

P = ma + Fms = 800 + 1000 = 1800 N

A = 1800 . 45 = 81000 J

P = \(\frac{81000}{15}\) = 5400W

\(\)