PHYSICS HELP NEEDED - MOVING ABOUT !!!!! (1 Viewer)

[superSAIyan2]

1. Explain why total momentum is conserved in a collision between two cars. [Must refer to Newtons 3rd Law] 4M

2. Identify a physicist and outline how that person has contributed to the developmenty of ideas in physics. 2M

3. A bowling ball weighing 10kg on the surface of Earth is taken to the moon where it weighs 1.6kg. 3M

For the first question I think that due to the third law the force each car exerts on the other is equal and thus they have the same impule (change in momentum) But how would I relate this to the law of cons of momentum?
For the second question I wrote about Newtons Laws and car safety mechanisms.
And for the third one I understand that its false cos kilograms is a measure of mass and newtons is for weight and that the mass of an object is irrespective of location and thus is constant. but its kinda confusing to word it into a proper response - cos theres so many things wrong with that statement. Lol.
How can I improve on my points and write a better response.

 

[deswa1]

1. Explain why total momentum is conserved in a collision between two cars. [Must refer to Newtons 3rd Law] 4M

2. Identify a physicist and outline how that person has contributed to the developmenty of ideas in physics. 2M

3. A bowling ball weighing 10kg on the surface of Earth is taken to the moon where it weighs 1.6kg. 3M

For the first question I think that due to the third law the force each car exerts on the other is equal and thus they have the same impule (change in momentum) But how would I relate this to the law of cons of momentum?
For the second question I wrote about Newtons Laws and car safety mechanisms.
And for the third one I understand that its false cos kilograms is a measure of mass and newtons is for weight and that the mass of an object is irrespective of location and thus is constant. but its kinda confusing to word it into a proper response - cos theres so many things wrong with that statement. Lol.
How can I improve on my points and write a better response.

I'll answer this one to show how I'd write it in an exam:
- This statement is wrong because it confuses weight with mass.
- Weight is a measure of the force that an object exerts due to gravity, according to the formula W=mg
- Mass is a measure of the objects inertia, in essence the amount of 'matter' present in a body
- Mass is constant everywhere and is measured in kilograms whilst weight varies based on the strength of a gravitational field and is measured in N.
- If the bowling ball had a mass of 10kg on Earth, it would have a weight of approximately 98N as g=9.8m/s/s. This same bowling ball would have a mass of 10kg on the Earth (as its inertia hasn't changed) but would have a weight of approximately 16N as g=1.6m/s/s

 

[bleakarcher]

For the first question my answer would probably be something like this.
By Newton' third law of motion, for every action there is an equal and opposite reaction i.e. for every force exerted upon a body the body exerts the same force but in opposite direction. In the case of two colliding cars, the first car exerts a force on the second car and so by the 3rd law the second car exerts a force of equal magnitude to the first towards the first car. Let the force which the first car (mass m1 and acceleration a1) exerts upon the second be F1 and the second (mass m2 and acceleration m2) on the first F2. By action=-reaction:
F1=-F1
i.e. m1a1=-m2a2
m1[(v1-u1)/(delta(t))]=-m2[(v2-u2)/(delta(t)] where u1 and u2 are the intial velocities of the two cars and v1 and v2 are the final velocities of the two cars, delta(t) being the small interval of time in which the collision occurs
Rearranging the equation:
m1u1+m2u2=m1v1+m2v2
Hence, the sum of the two initial momemtums in the two cars must be equal to the sum of the two final momemtums of the two cars. Hence, in the collision, momemtum is conserved. The momentum of the two cars may have changed but the total impulse (change in momentum) after the collision was zero.

 

[bleakarcher]

This is assuming a closed system in the collision between the two cars btw.

 

[superSAIyan2]

Yes the system is closed