Question

a trolley of mass 400g is moving at a constant velocity of 2.5m/s on a straight road. calculate the kinetic energy of the trolley​

Answer 1

Answer:

Mass of the trolley, M=200kg

Speed of the trolley, v=36km/h=10m/s

Mass of the boy, m=20kg

Initial momentum of the system of the boy and the trolley

=(M+m)v

=(200+20)×10

=2200kg m/s

Let v

′

be the final velocity of the trolley with respect to the ground.

Final velocity of the boy with respect to the ground =v

′

−4

Final momentum =Mv

′

+m(v

′

−4)

=200v

′

+20v

′

−80

From the conservation of linear momentum:

Initial momentum= Final momentum

2200=220v

′

−80

∴ v

′

=2280/220=10.36m/s

Length of the trolley, l=10m

Speed of the boy, v

′′

=4m/s

Time taken by the boy to run, t=10/4=2.5s

∴ Distance moved by the trolley =v

′′

×t= 10.36×2.5=25.9m

Answer 2

Answer:

25.9m

Explanation:

Mass of the trolley, M=200kg

Speed of the trolley, v=36km/h=10m/s

Mass of the boy, m=20kg

Initial momentum of the system of the boy and the trolley

     =(M+m)v 

     =(200+20)×10

     =2200kg m/s

Let v′ be the final velocity of the trolley with respect to the ground.

Final velocity of the boy with respect to the ground  =v′−4

Final momentum =Mv′+m(v′−4)

                             =200v′+20v′−80

From the conservation of linear momentum:

Initial momentum= Final momentum

                  2200=220v′−80

                    ∴ v′=2280/220=10.36m/s

Length of the trolley, l=10m

Speed of the boy, v′′=4m/s 

Time taken by the boy to run, t=10/4=2.5s

∴ Distance moved by the trolley =v′′×t= 10.36×2.5=25.9m