- Messages
- 300
- Reaction score
- 138
- Points
- 53
15: It is A simply because the ball's energy is being converted from kinetic to gravitational, since there is no air resistance, none of the ball's energy is being lost to the air as heat. So, the ball's energy is conserved. B is incorrect because the option says that the momentum of the ball is conserved. This is incorrect because the momentum of the ball and AIR/EARTH is being conserved. The momentum being lost by the ball is being gained by the air on earth(the ball is pushing the air causing it to flow with a velocity meaning it is getting momentum). C is incorrect because at max height, the velocity is zero so the kinetic energy must be zero. D is incorrect because the potential energy(they mean the gravitational energy) is increasing but not at a constant rate since the ball is slowing down(due to gravity). So the rate at which the ball is gaining height is decreasing until it reaches a max, so the ball's potential energy is increasing but not at a constant rate.View attachment 64067
Shouldn't D be correct here as the air resistance is negligible and using the equation s=ut + 0.5at² isn't it possible?
View attachment 64068
8: There is acceleration so there must be a resultant force. This rules out A which states that the upward and downward forces are equal. The force exerted by the man on the floor is an upward force, contact force. Since the acceleration is downwards, the resultant force must also be acting downwards. This means that the downward force is greater than the upward force(weight>contact force). The option that states this idea is D, so that's the answer.