How Do You Solve Motion and Collision Problems in Grade 12 Physics?

[hoooossein]

hi I am taking grade 12 physics and i have 2 quesions which I am not sure about.

1) a 45 kg student stand on a staitionary 33 kg raft. the student walks with a velocity of 1.9m/s [E] relative to the water. what is the resulting velocity of the raft, relative to the water, if fluid friction is negligible?
for this i thought it would be that the raft would be moving 1.9 m/s [w] because it will stay staitionary while the student walks [E]. am i right?

2) There is an elastic collision of two balls on a frictionless table. ball A has a mass of .5 kg and ball B has a mass of .3 kg. Ball A has an initial velocity of 4 m/s in the positive x-direction and a final velocity of 2 m/s in an unknown direction. ball B is initially at rest. Determine the final speed of Vb2 ball B and the angles Alpha and Bata.

the ball goes straight hits on and they both go forth but in different directions.
-- O
ball a ball b -- ball a
-----O>------o ----------
-- ball b
-- o

i actually don't have enoguh physics background to do this one. so if neone knows how please help me on this.

 

[Toftarn]

Use conservation of momentum on the first one. If they are both at rest at the beginning, and the student starts walking, then the boat will get a momentum that is exactly
as large as the student's, but in the opposite direction (inverted signs).

As for the second one, I'm not really sure what you are asking, so all I can really tell you is that you should keep in mind that both momentum and energy is conserved in an elastic collision.

 

[baba89]

I would like to commend you for taking an interest in physics and attempting these questions. Let me provide some explanations and solutions for both questions.

1) In this question, the student is walking on a stationary raft. Since the fluid friction is negligible, we can assume that the forces acting on the system are balanced and there is no external force acting on the raft. This means that the momentum of the system should remain constant. Therefore, we can use the law of conservation of momentum to solve this problem.

According to the law of conservation of momentum, the total momentum of a system remains constant unless acted upon by an external force. In this case, the initial momentum of the system is 0, as both the student and the raft are stationary. When the student starts walking with a velocity of 1.9 m/s [E], the momentum of the system will change. However, since there is no external force acting on the system, the final momentum should also be 0.

Therefore, the final velocity of the raft, relative to the water, would be -1.9 m/s [W]. This means that the raft will move in the opposite direction of the student's movement, with the same magnitude of velocity.

2) This question involves an elastic collision between two balls on a frictionless table. In an elastic collision, both kinetic energy and momentum are conserved. This means that the total kinetic energy before the collision is equal to the total kinetic energy after the collision.

To solve this problem, we can use the equations for conservation of momentum and conservation of kinetic energy. The initial momentum of the system is given by:

Pinitial = ma * va + mb * vb = (0.5 kg) * (4 m/s) + (0.3 kg) * (0 m/s) = 2 kg*m/s

The final momentum of the system is given by:

Pfinal = ma * va' + mb * vb' = (0.5 kg) * (2 m/s) + (0.3 kg) * (vb' cosα) = 1 kg*m/s

Since momentum is conserved, we can equate these two equations and solve for vb' cosα:

2 kg*m/s = 1 kg*m/s
vb' cosα = 1 m/s

Similarly, using the equation for conservation of kinetic energy, we can solve for vb' sinα:

KEinitial = KEfinal