Work Energy and Power - Online Test
Q1. in an elastic collision
Answer : Option D
Explaination / Solution:
kinetic energy is transferred to other forms of energy—such as thermal energy, potential energy, and sound—during the collision process. After collision if recovery of kinetic energy is 100% then it is called elastic collision.So that in an elastic collision the total kinetic energy of the system is the same after the collision as before.
Q2. in an inelastic collision
Answer : Option A
Explaination / Solution:
kinetic energy is transferred to other forms of energy—such as thermal energy, potential energy, and sound—during the collision process. After collision if recovery of kinetic energy is less than % then it is called inelastic collision i.e.. some part of kinetic energy is not recover. So that in an inelastic collision the total kinetic energy after the collision is less than before the collision
Q3. In a completely inelastic collision
Answer : Option A
Explaination / Solution:
For perfectly Inelastic collision coefficient of restitution is zero.
coefficient of restitution e= relative velocity of separation / relative velocity of approach
e = 0
so that relative velocity of separation will be zero means the colliding bodies stick together and move as one body after the collision
Q4. In which of the following cases is the work done positive?
Answer : Option C
Explaination / Solution:
Work done is positive when force applied and displacement are in same direction.
in this case angle between force and displacement is zero (i.e. ) so that work done is positive.
Q5. In which of the following cases is the work done positive?
Answer : Option C
Explaination / Solution:
Work done is positive when force applied and displacement are in same direction.
in this case angle between force and displacement is zero (i.e. ) so that work done is positive.
Q6. The casing of a rocket in flight burns up due to friction. At whose expense is the heat energy required for burning obtained?
Answer : Option A
Explaination / Solution:
Heat energy required for burning of casing of rocket comes from the rocket itself. As a result of work done against friction the kinetic energy of rocket continuously deceases and this work against friction reappears as heat energy. This results in reduction of the mass of the rocket.
Q7. A body constrained to move along the z-axis of a coordinate system is subject to a constant force F given by , wher are unit vectors along the x-, y- and z-axis of the system respectively. What is the work done by this force in moving the body a distance of 4 m along the z-axis?
Answer : Option D
Explaination / Solution:
given that
Q8. Balram exerts a steady force of magnitude 150 N on the stalled car as shown in the figure below; he pushes it a distance of 20 m. The car also has a flat tyre, so to make the car move straight. He pushes at an angle of 30 to the direction of motion. How much work does he do?
Answer : Option B
Explaination / Solution:
W=Fscosθ=150×20×
3√2=2598J
Q9. Balram exerts a steady force of magnitude F = 200+ 2.0 on the stalled car as shown in the figure above, he pushes it a distance s = 10 + 10 m. How much work does he do?
Answer : Option D
Explaination / Solution:
F⃗ =200i^+2
s⃗ =10i^+10
W=F⃗ .s⃗ =(200i^+2j^).(10i^+10j^)
W=2000+20=2020J
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Q10. A railway porter is holding a weight of 100 kgs on his head and is standing still. What is the work done by him?
Answer : Option A
Explaination / Solution:
W = Force x displacement in the direction of force
Work done will be zero because porter is stationary (i.e. displacement is zero)
