A force of 20000N acts on the raft in the direction down State the name given to the force shown by arrow in Fig.
Calculate the mass of the raft.

Figure is not there

Explanation:

d. air pressure decreases as altitude increases.

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me