þ. When a train is traveling along a straight track at 2 m/s, it begins to accelerate at a = (60 v) m/s², where v is in m/s. Determine its velocity v and the position 3 s after the acceleration. 3. A sphere is fired downwards into a medium with an initial speed of 27 m/s. If it experiences a deceleration of a-(-6t) m/s², where t is in seconds, determine the distance travelled before it stops. Question 13.7 If the 50-kg crate starts from rest and travels a distance of 6 m up the plane in 4 s, determine the magnitude of force acting on the crate. The coefficient of kinetic friction between the crate and the ground is = 0.25. Answer: P = 391 N Question 13.9 The crate has a mass of 80 kg and is being towed by a chain which is always directed at 20° from the horizontal as shown. If the magnitude of P is increased until the crate begins to slide, determine the crate's initial acceleration if the coefficient of static friction is = 0.5and the coefficient of kinetic friction is k=0.3. Answer: a=1.66 m/s²