Sin A screw jack is used to raise a body of mass 6000kg through a height of
0.25m by turning its tommy bar through 30 revolutions. If the length of its
tommy-bar. is 0.75m and the jack is 85% efficient, calculate
(ii)
its velocity ratio,
the effort required to raise the body.
[T = 3.14, g = 10ms)​

Atruck going 15 kmôź°€h has a head-on collision with a small car going 30 kmôź°€h. which statement best describes the situation? (a) the truck has the greater change of momentum because it has the greater mass. (b) the car has the greater change of momentum because it has the greater speed. (c) neither the car nor the truck changes its momentum in the collision because momentum is conserved. (d) they both have the same change in magnitude of momentum because momentum is conserved. (e) none of the above is necessarily true. 2. 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) increases. (b) decreases. (c) does not change. (d) without knowing the mass of the boat and the sand, we can’t tell.