A 400 kg rocket sled can be accelerated at a constant rate f

A 400 kg rocket sled can be accelerated at a constant rate from rest to 1400 km/h in 1.9 s. What is the magnitude of the required net force? A lamp hangs vertically from a cord in a descending elevator that decelerates at 2.8 m/s^2,If the tension in the cord is 88 N, what Is the lamp\'s mass? What is the cord\'s tension when the elevator ascends with an upward accolorition of 2.8 m/s^2?

Solution

Mass of rocket m = 400 kg

Initial speed u = 0

Final speed v = 1400 km/h

                    = 1400(1000m)/(3600s)

                    = 388.88 m

Time t= 1.9 s

Net force F = m(v-u)/t

                 = 400(388.88-0)/1.9

                 = 81871.34 N

(2) Given a = -2.8m/s ²

(a).Tension T = 88 N

mg-T = ma

m(g-a) = T

       m = T /(g-a)

            = 88 /(9.8-(-2.8))

            = 88 /(12.6)

            = 6.98 kg

(b).Tension T = ?

T-mg = ma

       T = ma +mg

          = m(a+g)

          = 6.984(2.8+9.8)

          = 88 N