A small boat coasts at constant speed under a bridge. A heavy sack of sand is dropped from the bridge onto the boat. The speed of the boat:
a) A small boat coasts at constant speed under a bridge.
b) A heavy sack of sand is dropped from the bridge onto the boat.
c) The speed of the boat decreases.
d) increases.
e) does not change.
f) Without knowing the mass of the boat and the sand, we can't tell.

Explanation:

Let the mass of boat is m ad the initial velocity of the boat is u, the mass of sack is M and the velocity of boat after the sack is dropped in it is V.

As there is no external force acting on the system, so the linear momentum is conserved.

m x u = ( M + m) V

V = mu / ( M + m)

So, as M > m and the denominator is more than numerator so the velocity of the boat decreases.

Option (c) is correct.

a longitudinal wave moves energy that is to the direction of the wave’s movement. - true

v=ir = 3x15 =45 v