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1) Three bricks are thrown from the roof of a building with the same speed but with different launch angles: one above the horizontal, one below the horizontal and one horizontal. Assuming no air resistance, which brick has the highest speed by the time it reaches the ground?

My answer: Simple conservation of energy... mgh = 0.5mv^2. They all have the same velocity... is this correct? Just wanted to confirm

2) If 2 cars crash, which would you expect to be more harmful to the passengers: if the cars crash and stay together, or if the cars collide and rebound backward? Explain.

My answer: Honestly, I am not sure at all. Momentum is conserved in both, thus impulse is 0. Only thing is... energy is lost in a sticky collision, so I'm going with an inelastic collision. However, I cannot explain it.

3) Can the total mechanical energy be negative? E = KE + PE

Explain + provide an example.

My answer: I always learned that energy is positive. But I'm thinking this can depend on the point of reference. If my reference point is 1000m above a cliff, the potential energy of a rock on the cliff is negative and has no kinetic energy... so E is -ive.

My answer: Simple conservation of energy... mgh = 0.5mv^2. They all have the same velocity... is this correct? Just wanted to confirm

2) If 2 cars crash, which would you expect to be more harmful to the passengers: if the cars crash and stay together, or if the cars collide and rebound backward? Explain.

My answer: Honestly, I am not sure at all. Momentum is conserved in both, thus impulse is 0. Only thing is... energy is lost in a sticky collision, so I'm going with an inelastic collision. However, I cannot explain it.

3) Can the total mechanical energy be negative? E = KE + PE

Explain + provide an example.

My answer: I always learned that energy is positive. But I'm thinking this can depend on the point of reference. If my reference point is 1000m above a cliff, the potential energy of a rock on the cliff is negative and has no kinetic energy... so E is -ive.

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