if work is a scalar quantity then how it can take neagtive values ?????
For example, the numbers on a thermometer Celsius scale which measures temperature. These values require a positive or negative sign to indicate whether they are greater or less than zero, but they do not require an indication of direction because they have no component which describes their location in space.
Work is dot product of force vector and displacement vector, which have directions in space and magnitude of work is negative when angle between force and displacement is more than 90 degrees.