Question

What happens when :
(a) force is applied in the direction of motion.
(b) force is applied in the direction opposite to the motion.
(c) two equal forces act in direction opposite to each other.
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Answer 1

(a) The force will produce displacement and the work done will be positive .

(b) The force will produce negative work .

(c) The net force is zero and hence there would be no acceleration .

NOTE :

Work done = force × displacement × component of work .

Component of work is cos Ф since the work done is a scalar product of two vectors .

When forces act in opposite direction , Ф = 180° which makes cosФ = - 1 .

When forces act in same direction Ф = 0° and cos 0° = 1 .

Similarly cos 90° = 0 .