Question

A force of 50N acts on a body of mass 2kg at rest for 10seconds . how much force is required to bring the body into rest 5seconds
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Answer 1

Answer:

100N

Explanation:

Method 1 (mass is irrelevant):

50N acting for 10s is an impulse of 500Ns, giving the object a momentum of 500kgm/s.

To lose this much momentum and return to stationary requires an opposing impulse of 500Ns.

To occur in 5s this requires a force of 100N.

Method 2:

F=ma gives an initial acceleration of 25m/s2.

The SUVAT expression v=u+at gives a speed of 250m/s.

In order to stop in 5s, v=u+at shows an acceleration of 50m/s2 is required.

F=ma gives a required force of 100N.