a man 100 kg is standing on a platform of mass 200 kg which is kept on ice surface.If the man starts moving with speed 30m/s relative to the platform then,find what velicity relative to ice the platform will recoil ??
Anonymous:
Am I to assume that there is no friction between ice surface and platform?
as it is not stated, we assume that way
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Momentum of the man + platform is a constant and is 0. Reason is that there is no net external force acting on this system. Hence as per Newton's 2nd law, the momentum is conserved.
We take the velocities wrt to ice (static/inertial reference). Let velocity of the recoil of the platform be V m/s. Then the man is moving wrt the ice in the opposite direction at (30-V) velocity.
100 * (30-V) - 200 * V = 0
300 V = 3000
Recoil velocity V = 10 m/s in the opposite direction of movement of the man.
Velocity of the man wrt to ice = 20m/s
(Their relative velocity = 30 m/s)
We take the velocities wrt to ice (static/inertial reference). Let velocity of the recoil of the platform be V m/s. Then the man is moving wrt the ice in the opposite direction at (30-V) velocity.
100 * (30-V) - 200 * V = 0
300 V = 3000
Recoil velocity V = 10 m/s in the opposite direction of movement of the man.
Velocity of the man wrt to ice = 20m/s
(Their relative velocity = 30 m/s)
Nice sir!!
thanx for pointing it out. i missed that point.
How did you take that momentum of man + platform system is zero?
when both were at rest, there is no horizontal momentum. Man gets velocity/acceleration by exerting force on platform, Platform exerts equal and opposite force. so net force on the total system is 0. if net force is zero, the momentum is conserved.
Okay then
the answer is 10 m/s
when i do the problem with cm
what do u mean ?
i solved the sum with center of mass
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