Calculate Change in Momentum of 65kg Runner After Half Revolution

[Masafi]

A runner of mass 65kg is running around a circular track at 5m/s. What is the magnitude of the change in his momentum from start to end after half a revolution?

My answer if 650Ns, but the answer is written as 625Ns.

 

[Stonebridge]

I would say you are correct.
The momentum changes from +325Ns to -325Ns

 

[kerimek]

I would like to clarify the calculations for the change in momentum in this scenario. The change in momentum is equal to the final momentum minus the initial momentum, which can be represented as Δp = p_final - p_initial. In this case, the runner's initial momentum can be calculated as p_initial = m x v = 65kg x 5m/s = 325kgm/s. After half a revolution, the runner's final velocity would be in the opposite direction, so we can calculate p_final as p_final = m x (-v) = 65kg x (-5m/s) = -325kgm/s. Therefore, the change in momentum would be Δp = (-325kgm/s) - (325kgm/s) = -650kgm/s. It is important to note that the negative sign indicates a change in direction, which is expected as the runner completes half a revolution. Therefore, the magnitude of the change in momentum would be 650kgm/s. I believe this is the correct answer based on the given information.