Question

A body of mass 0.40 kg moving initially with a constant speed of 10 m/s to the North is subjected to a constant force of 8.0 N directed towards the South for 30 S. Take the instant the force is applied to be t = 0, the position of the body at that time to be x = 0, and predict its position at t = -5s and 25s.

Answer 1

Answer:

Given mass m =0.4 kg

Retarding force F = -8 N

∴ acceleration a=

m

F

=

0.4

−8

=−20m/s

2

at t = -5 s

a = 0 for t < 0

∴s=u+

2

1

at

2

=10(−5)+

2

1

(0)(−5)

2

at t = 25 s

S=ut+

2

1

at

2

= 10(25)+

2

1

(−20)(25)

2

=−6000m

at t = 100 s

since there is a retarding force for 30 s

S

1

=ut+

2

1

at

2

=10(30)+

2

1

(−20)(30)

2

=−8700m

after 30 s it move with a constant velocity

V= u + at

= 10 - 20 (30)

= -590 m/s

for rest of 70 s

S

2

=−590(70)+

2

1

(0)(70)

2

=−41300m

∴ Total distance = S

1

+S

2

=50000