NEET | 2018Laws of MotionHard

Question

A toy car with charge q moves on a frictionless horizontal plane surface under the influence of a uniform electric fieldE. Due to the force qE , its velocity increases from 0 to 6 m/s in one second duration. At that instant the direction of the field is reversed. The car continues to move for two more seconds under the influence of this field. The average velocity and the average speed of the toy car between 0 to 3 seconds are respectively :-

Options

A.

2 m/s, 4 m/s

B.

1 m/s, 3 m/s

C.

m/s, 3.5 m/s

D.

1.5 m/s, 3 m/s

Solution

0 < t < 1s : velocity increases from 0 to 6 m/s 1 < t < 2s : velocity decreases from 6 to 0 m/s but car continues to move forward 2 < t < 3s : since field strength is same
same acceleration  car's velocity increases from 0 to –6 m/s

Distance travelled in first second
S=u+v2t=0+621=3m
Distance = 9 m so average speed =9m3s=3m/s
Displacement = 3m so average velocity =3m3s=1m/s

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