Q6 of 40 Page 109

A constant force acting on a body of mass 3.0 kg changes its speed from 2.0 m s-1 to 3.5 m s-1 in 25 s. The direction of the motion of the body remains unchanged. What is the magnitude and direction of the force?

The first equation of motion is given as :


v = u + at …….(i)


where,


v is the final speed,


u is the initial speed,


a is the acceleration of the body.


t is the time taken by the body.


Given,


Mass of the body, m = 3 kg


Initial speed of the body, u = 2 m/s


Final speed of the body, v = 3.5 m/s


Time taken by the body, t = 25 sec


From equation (i),


⇒


From Newton’s second law of motion, the magnitude of the force is given as,


F= ma


= 3 kg × 0.06 m/s2


⇒ F = 0.18 N


The magnitude of the force is 0.18 N and since the acceleration does not change the direction of the motion. The direction of the force is in the same direction of the motion.


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