(1) Use Newton's second law: The force <em>F</em> required to accelerate a mass <em>m</em> with acceleration <em>a</em> satisfies
<em>F</em> = <em>m a</em>
So the force needed to accelerate the lion-stretcher system is
<em>F</em> = (175 kg) (2 m/s²) = 350 N
(2) Average speed is defined as the ratio of distance traveled to the time it takes to travel that distance, so in this case the bus's average speed is
(280 km) / (4 h) = 70 km/h
(3) The vertical lines in the plot split up the distance function into 5-minute chunks. The one with the highest average speed is the one over which the distance changes the most. Roughly, the average speeds over each of the given choices is
• 0 to 5 min : (1500 m - 0 m) / (5 min) = 300 m/min
• 10 to 15 min : (3250 m - 2500 m) / (5 min) = 150 m/min
• 15 to 20 min : (3750 m - 3250 m) / (5 min) = 100 m/min
• 25 to 30 min : (4500 m - 4250 m) / (5 min) = 50 m/min
(4) Velocity is a vector, so it has both magnitude and direction. A car moving at constant velocity would be traveling at the same magnitude and direction. But a car on the circular track is constantly turning and changing direction.
