Test: Work And Energy

If a force acting on a body has a component in the direction of displacement, then the work done by the force is positive. Hence when a body falls freely under the influence of gravity the work done by the gravity is positive.

If X and Y have equal kinetic energy but their masses are m and 4m respectively. Thus we get the ratio of their speed is 2:1. Hence the ratio of their linear momentum is 1:2.

Work done, W = Force x Δdisplacement

So, when a person holds some amount of load but does not move from his position, the displacement is 0. Hence, W done = 0.

The work is zero because while the truck does have a displacement over time, the force of the road (the normal force) is perpendicular and so the dot product of the two is zero.

Energy The joule ( symbol: J) is a derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metreor N⋅m). 

We know that KE = ½ mv²
And as neither the mass nor v² can be negative.
We get KE cant be negative.

Every object that tends to fall or does fall on earth's surface does have a gravitational acceleration which is possessed by them due to their gravitational potential energy.

We know that Work done, W = F.s where F is force and s is displacement due to that force
Thus rate of work done = dW/dt = d(F.s)/dt
So as F is constant we get  dW/dt = F.d(s)/dt
= F.v = P

Changes(if required):
Solution:
η=50%= 50/100=1/2
So as we know, η=work output/heat input​
1/2=4500/Heat input
Heat input =9000J
 

If a force acting on a body has a component in the opposite direction of displacement, the work done is negative, when a body slides against a rough horizontal surface, its displacement is opposite to that of the force of friction. He work done by the friction is negative.