Read each statement below carefully and state with reasons and examples, if it is true or false ;
A particle in one-dimensional motion
(a) with zero speed at an instant may have non-zero acceleration at that instant
(b) with zero speed may have non-zero velocity,
(c) with constant speed must have zero acceleration,
(d) with positive value of acceleration must be speeding up.
(a) True.
Explanation: When an object is vertically thrown upwards, at maximum height its velocity becomes zero. However, its acceleration remains constant (acceleration due to gravity).
(b) False.
Explanation: Speed and velocity have same magnitude for a body. So, If a body is having zero speed it should have zero velocity.
(c) True.
Explanation: Acceleration is defined as change in velocity with respect to time. Thus, If change in velocity is zero acceleration is also zero.
(d) False.
Explanation: When a body is vertically thrown upwards. Even though positive acceleration the body have it will slowly speeding down due acceleration due to gravity.
True.
Explanation: When a body is freely falling from a height. Acceleration due to gravity speedup the body.