[填空题]
A robot is used to move boxes in a factory. A box is pulled up a slope inclined at $30^{\circ}C$ to the horizontal by a rope connected to the robot. The tension T in the rope is 45$\,N$. Friction acts between the box and the ramp.
1.Define work done by a force.
2.The box is moving at a constant speed. It covers $1.2\,m$ in $3.0\,s$.
(1).Show that the output power of robot $18\,W$.v= $ms^{−1}$
P= W
(2).During the pull, the robot has a potential difference of $24\,V$ across the terminals of its battery and a current of $3.3V$ derived from the battery. Determine the efficiency of the robot in this situation.$P_t$= W
$\frac{Useful Power}{Total Powe}$=
(3).The emf of the battery is 32 $V$. Calculate the internal resistance of the battery.
3.The rope connecting the robot and the box breaks at a height of $1.5\,m$ from the ground level.r= Ω
(1)The maximum height above the ground level reached by the box is $1.505\,m$. Show that the work done by friction on the box after the break up to reach the maximum height is $0.15\,J$.$W_f$= J
(2)Determine the coefficient of dynamic friction between the box and the incline.μ=
The box experiences friction both on the way up the slope and also as it slides back down the slope. On the graph below, sketch the variation of the speed $v$ of the box with the time $t$ passed from when the rope breaks until the box reaches the ground level.
