Momentum and the Conservation Laws

[closer]

A 4.00 kg steel ball strikes a wall with a speed of 9 m/s at an angle of 60.0° with the surface. It bounces off with the same speed and angle (Fig. P8.9) If the ball is in contact with the wall for 0.200 s, what is the average force exerted on the ball by the wall?

F$$\Delta$$T = $$\Delta$$p
p = mv

$$\Delta$$p = p_f - p_i = mv_f - mv_i = m(v_f - v_i)
$$\Delta$$p = m(v_f - v_i)
$$\Delta$$p = 4(-9 - 9)
$$\Delta$$p = -72
F_average$$\Delta$$t = $$\Delta$$p
F_average(.2) = -72
F_average = -360

Final answer is incorrect, any ideas?

 

[LowlyPion]

A 4.00 kg steel ball strikes a wall with a speed of 9 m/s at an angle of 60.0° with the surface. It bounces off with the same speed and angle (Fig. P8.9) If the ball is in contact with the wall for 0.200 s, what is the average force exerted on the ball by the wall?

F$$\Delta$$T = $$\Delta$$p
p = mv

$$\Delta$$p = p_f - p_i = mv_f - mv_i = m(v_f - v_i)
$$\Delta$$p = m(v_f - v_i)
$$\Delta$$p = 4(-9 - 9)
$$\Delta$$p = -72
F_average$$\Delta$$t = $$\Delta$$p
F_average(.2) = -72
F_average = -360

Final answer is incorrect, any ideas?

The only thing that reversed is the x-component of velocity.
The y-component remained the same and since you are taking differences in Vectors - Velocity is a vector after all - then the force should bbe determined off of the change in x-component of velocity.

 

[baba89]

I would first check the calculations to ensure they are correct. It seems that the final answer may be incorrect due to a sign error. The change in momentum should be positive, as the ball is bouncing off the wall in the opposite direction. Therefore, the average force exerted by the wall on the ball should also be positive.

Also, it is important to note that the angle of impact may affect the direction of the average force exerted on the ball. In this case, the angle of 60 degrees may result in a slightly different force than if the ball had struck the wall head-on.

Furthermore, it is important to consider the assumptions and limitations of the conservation laws in this scenario. The conservation of momentum assumes that there are no external forces acting on the system, which may not be entirely true in this case. Other factors such as air resistance and friction may affect the motion of the ball and the force exerted by the wall.

In conclusion, while the calculations may need to be reviewed and corrected, it is also important to consider the limitations and other factors that may affect the application of the conservation laws in this scenario.