A high-speed magnetic-levitation test sled travels along a straight horizontal track at a constant initial speed UUU. At time t=0t = 0t=0, the electromagnetic braking system is activated, and the sled is brought to a complete stop at t=4.0 st = 4.0\text{ s}t=4.0 s.
The graph below shows the variation of the braking force F F\,F on the sled with time ttt.
a.[2]
Use Newton's second law of motion to explain the physical quantity represented by the area under the FFF-t t\,t graph.
b.[3]
The total mass of the sled is 80 kg. Use the graph to calculate the initial speed UUU.
c.[3]
Describe the shape of the speed-time graph of the sled from t=0t = 0t=0 to t=4.0 st = 4.0\text{ s}t=4.0 s. State the initial and final coordinates on this graph.