Answer:

Force F=50N

Mass m=20kg

Initial velocity u=15m/s

Now, from newton’s second law

F=ma

50=20×a

a=2.5m/s

2

Now from equation of motion

v=u+at

0=15+(−2.5)t

t=

2.5

15

t=6s

Hence, the body will be stop in 6 sec.

B. Given that,

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, t=25 sec

Now, for acceleration

Use the equation of motion

v=u+at

a=

t

(v−u)

a=

25

3.5−2

a=

25

1.5

a=0.06 m/s

2

Now, for the force

Use the newton’s second law

F=ma

F=3×0.06

F=0.18 N

The magnitude of the force is 0.18 N.