[填空题]
A robot is used to move boxes qzmw (*a o,t-ein a factory. A box is pulled up a slo3o1 v5uucdz;ype inclined z3 u1udy5voc ;at $30^{\circ}C$ to the horizontal by a rope connected to the robot. The tension T in the rope is 45N. 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) Calculate the output power of robot. $P$ = $W$
(2) During the pull, the robot has a potential difference of $24\,V$ across the terminals of its battery and a current of $3.0\,A$ derived from the battery. Determine the efficiency of the robot in this situation. The efficiency(percentage) is: %
(3) The $emf$ of the battery is $32\,V$. Calculate the internal resistance of the battery. $r$ = $\Omega$
3.The rope connecting the robot and the box breaks at a height of $1.5\,m$ from the ground level.
(1) The maximum height above the ground level reached by the box is $1.505\,m$. Calculate the work done by friction on the box after the break up to reach the maximum height. $W_f$ = $J$
(2) Determine the coefficient of dynamic friction between the box and the incline. $\mu$ =
(3) 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.
