1. An 18.0 kg sled is slding across a smooth, flat stretch of snow when a boy pushes it, causing it to speed up to 4,50 m/s in 3.75 s without changing direction. If the average force exerted by the boy
on the sled in its direction of motion was 12,5 N, with what initial velocity was it moving?

Answertraveling around a circular trackexplanation"traveling around a circular track" is the best answer as you could be traveling around a circular track at a constant speed. your velocity would therefore have the same magnitude but will always be constantly direction. since acceleration is the rate of change of velocity, the rate of change will only involve the direction of velocity and not the magnitude.wrong choices: "an object at rest" does not accelerate at all"increasing speed while traveling around a curve" means that the acceleration will not be constant due to only change in direction; it will be constant due to both magnitude and direction"an object in free fall" does not necessarily change direction 

The particles of the gas inside the ball heats up, bouncing off each other and spreading farther apart.hope my answer has you : )