Conservation of Energy and Momentum MCQ

The conservation of energy and momentum is one of physics’ most significant and practical ideas. The law of conservation of momentum asserts that if a system of bodies is not subjected to any net external pressures, its overall momentum remains constant at all times (it is conserved). Furthermore, if all external and internal forces can be given a potential, the total energy remains constant; this is the law of conservation of energy.

The conservation laws, although their fundamental nature, are often difficult to observe in everyday life, owing to the presence of friction. Friction between moving bodies and their surroundings indicates that an external force is operating on them, negating the application of conservation of momentum. Furthermore, because a potential energy for the force of friction cannot be specified, energy is not conserved when friction is present. Friction must be reduced as much as feasible in order to follow the conservation regulations.

This lab will largely focus on the conservation rules as they apply to material item collisions. Depending on whether or not kinetic energy is conserved, such collisions can be classified into two groups. If the only forces between two particles exist when they collide, then the kinetic energy must be the same before and after the collision (when no net forces exist). Solid bodies, on the other hand, are not particles but rather have a structure.

If the structure of two objects remains intact after a collision, they can be securely considered as particles. This is known as an elastic collision, and kinetic energy is preserved in this situation. If this is not the case, energy may flow into the structure of a body in ways that do not contribute to its overall motion, such as when huge a large number of atoms are rearranged or moved.. When this occurs, the collision is considered to be inelastic, and the bodies’ kinetic energy is not preserved. It’s worth noting that in the absence of friction or other external forces, momentum for both types of collisions will be preserved.

Q1. A collision occurs when two bodies moving at the same speed collide. Which of the following quantities has not been lost?
a) Momentum
b) Speed
c) Force
d) Velocity

Answer: a) Momentum as in the absence of any external force, two bodies collide. The momentum will remain constant in this scenario because there is no force, hence there will be no change in momentum. After a collision, the bodies’ velocity and speed may alter.

Q2. A steady velocity is maintained by a ball. It eventually collides with a wall. Except for momentum, which of the following remains conserved?
a) Energy
b) Displacement
c) Power
d) Force

Answer: a) Energy as aside from momentum, energy is also preserved during a collision. In truth, a system’s energy is frequently preserved.

Q3. What is the new mass of a variable mass body with an initial mass of 5 kg moving at a velocity of 5 m/s for a short time before increasing to 10 m/s? If the body is moving without any external force, what is the new mass?
a) 2.5 Kg
b) 5 Kg
c) 7.5 Kg
d) 10 Kg

Answer: a) 2.5 Kg
The momentum of the body is conserved since it is travelling in the absence of any external force.

m1v1=m2v2 ………..(i)

In this scenario,

v1=5m/s m1=5kg v2=10 m /s

Putting the values in equation (i) we get m2=2.5 kg

Q4. Two bodies of masses 2 Kg and 7 Kg are moving with velocities of 2 m/s and 7 m/s respectively. What is the total momentum of the system in Kgm/s?
a) 50
b) 53
c) 28
d) 0

Answer: b) 53
Because both bodies are travelling at the same rate, they have the same amount of momentum. The sum of the momenta of the bodies is the system’s momentum.

Therefore, total momentum = (2 x 2) + (7 x 7) = 53 Kgm/s.

Q5. What does the word ‘momentum’ mean in plural?
a) Momenta
b) Momentums
c) Moments
d) Momentum

Answer: a) Momenta
Momenta, not momentums, is the plural of momentum. Momenta is a plural word that is typically employed when we need to address many momentums. In systems with more than one moving body, this condition may occur.

Q6. Two bodies are rapidly approaching each other. They eventually clash. Which of the following statements regarding the system is correct?
a) Around the time of collision, the whole momentum is conserved.
b) During a collision, the overall momentum is conserved.
c) The overall momentum of the system is not conserved.
d) The complete momentum is maintained.

Answer: a) Around the time of collision, the whole momentum is conserved.
The two bodies collide as they accelerate. The overall momentum does not remain preserved during the motion since they are accelerating. However, both bodies have the same velocity at the time of collision. As a result, the overall momentum will be conserved shortly before and after the impact.

Q7. What assumptions do we make when a body collides with a wall or the ground?
a) The body has a significant mass
b) The body is stationary
c) When compared to the mass of the wall or the ground, the body’s mass is insignificant.
d) The body is perfect

Answer: c) When compared to the mass of the wall or the ground, the body’s mass is insignificant.

When a body collides with a wall or the ground, we regard the body’s mass to be little in comparison to the wall’s or the ground’s mass. We also assume this when a feather, which has a very small mass, collides with a truck, which, in comparison, has a very large mass.

Q8. What is the new mass of a body with an initial mass of 10 kg moving at a velocity of 7 m/s for a short time before increasing to 14 m/s? If the body is moving without any external force?
a) 2.5 Kg
b) 5 Kg
c) 7.5 Kg
d) 10 Kg

Answer: b) 5 Kg
Explanation: The momentum of the body is conserved since it is travelling in the absence of any external force.

m1v1=m2v2 ………..(i)

In this scenario,

v1=7m/s m1=10 kg v2=14 m /s

Putting the values in equation (i) we get m2=5 kg

Q9. Which of the statements below is correct?
a) Kinetic energy and momentum both are conserved in all types of collisions.
b) In inelastic collisions, total kinetic energy is not preserved, but momentum is.
c) In elastic collisions, momentum is conserved, but not in inelastic collisions.
d) Inelastic collisions save total kinetic energy, whereas elastic impacts do not conserve momentum.

Answer: b) In inelastic collisions, total kinetic energy is not preserved, but momentum is.