WORK ENERGY AND POWER Quiz-18
Dear Readers,
Work power energy is the most important chapter when it comes to mechanics, for JEE (Advanced). The chapter is quite tricky and takes a lot of time and devotion on your part to understand and master. But this chapter is a complete gold medal for almost all the questions of the mechanics can be solved by the work power energy approach if you master this topic..
Q1.
Statement 1: According to law of conservation of mechanical energy change in potential energy is equal and opposite to the change in kinetic energy
Statement 2: Mechanical energy is not a conserved quantity
Solution
For conservative forces the sum of kinetic and potential energies at any point remains constant throughout the motion. This is known as law of conservation of mechanical energy. According to this law,
Kinetic energy + Potential energy = constant
Or, ∆K+∆U=0 or, ∆K=-∆U
Q2.
Statement 1: Work done by friction depends upon displacement of the body
Statement 2: Frictional force is non-conservative
Solution
Work done by non-conservative force depends upon the entire path, i.e., distance
Q3.
Statement 1: In an elastic collision of two bodies, the momentum and energy of each body is conserved
Statement 2: If two bodies stick to each other, after colliding, the collision is said to be perfectly elastic
Solution
In an elastic collision both the momentum and kinetic energy remains conserved. But this rule is not for individual bodies, but for the system of bodies before and after the collision. While collision in which there occurs some loss of kinetic energy is called inelastic collision. Collision in daily life are generally inelastic. The collision is said to be perfectly inelastic, if two bodies stick to each other
Q4.
Statement 1: A body is connected to a straight and if it just complete a circle, it must have zero velocity at the top
Statement 2: A body is projected in vertically upward direction, at the highest point the acceleration of the particle is non-zero
Solution
At the highest point of vertical circle tension is zero, not velocity
Q5.
Statement 1: Wire through which current flows gets heated
Statement 2: When current is drawn from a cell, chemical energy is converted into heat energy
Solution
When we supply current through the cell, chemical reactions takes place, so chemical energy of cell is converted into electrical energy
Q6.
Statement 1: Power developed in circular motion is always zero
Statement 2: Work done in case of circular motion is zero
Solution
Work done and power developed is zero in uniform circular motion only
Q7.
Statement 1: The changes in the kinetic energy of a particle is equal to the work done on it by the net force
Statement 2: The change in kinetic energy is equal to the work done only in case of a system of one particle
Solution
∆KE=W(by net force)
This relation is valid for particle as well as system of particles
Q8.
Statement 1: Power of machine gun is determined by both, the number of bullet fired per second and kinetic energy of bullets
Statement 2: Power of any machine is defined as work done (by it) per unit time
Solution
K.E. of one bullet =k ∴ K.E. of n bullet =nk
According to law of conservation of energy, the kinetic energy of bullets be equal to the work done by machine gun per sec
Q9. Statement 1: Work is always same in all the reference frames as it is an invariant physical quantity
Statement 2: Work is a dot product of force and displacement and, therefore, work is variant because force and displacement are dependent on frames of reference
Solution
Q10. Statement 1: Power developed in a uniform circular motion is always zero
Statement 2: Work done in case of a uniform circular motion is zero
Solution
Work done and power developed is zero in uniform circular motion
p=W/t, hence reason is the correct explanation of assertion
