Physics
Assertion (A) : Acceleration of a moving body is always positive.
Reason (R) : Acceleration is the rate of change of velocity with time.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Related Questions
Assertion (A) : The slope of displacement-time graph gives the velocity.
Reason (R) : Velocity is the product of displacement and time.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Assertion (A) : The velocity-time graph of a body in motion can be a straight line parallel to the time axis.
Reason (R) : This is because the motion of body is with non-uniform velocity.
- Both A and R are true and R is the correct explanation of A
- Both A and R are true and R is not the correct explanation of A
- Assertion is false but reason is true
- Assertion is true but reason is false
Assertion (A) : The acceleration-time graph of а body is a straight line parallel to time axis.
Reason (R) : This depicts the motion of freely falling body under gravity.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
A lift starts from rest at the ground floor and moves vertically upward along a straight shaft. During the first 4 s, the lift moves with uniform acceleration and attains a velocity of 2 m s-1. It then moves with uniform velocity for the next 6 s. Finally, it is brought to rest uniformly in 2 s at the top floor.
Assuming the motion to be one-dimensional, answer the following:
(a) Calculate the acceleration of the lift during the first 4 s.
(b) Calculate the total height between the ground floor and the top floor.
(c) Draw the velocity-time graph for the complete motion and mark the regions of acceleration, retardation and zero acceleration.
(d) Use the graph to calculate the average velocity of the lift during the upward journey.
(e) If the lift now moves downward following the same pattern, how would the signs of acceleration and displacement change?
(f) "The lift has maximum acceleration when it starts moving." Is this statement correct? Give reason.