Answer:
If the system consists of the block only, the work done by the gravity is negative.
If the system consists of the block and the earth the work done by the gravity is zero.
Explanation:
If the system consists of the block only, then the system experiences two external forces: one exerted by the hand that lifts the block vertically upward and other exerted by the earth (gravity), which is opposed to the movement of the system, so the work done by gravity is negative.
On the other hand, if the system consists of the block and the earth, then only exists a external force which is the exerted by the hand. So, the force exerted by gravity is zero.
Answer:
Sorry I'm wrong The person above is correct.
I tried.
Answer:
towards west
Explanation:
As we know that the speed of the blue car as appear to the bicycle rider is given as
towards west
also it is given that bicycle is moving at speed of 10 km/h towards East
so here we have

so we have

towards west
now speed of the red car is given as 15 km/h towards west
so here the relative speed of blue car with respect to red car is given as

towards west