12. suppose a person uses a mechanical iack to lift half the weight of a car with a
mass of 1200 kg. during each stroke of the jack handle, the person's hand is
pushing for a distance of 40.0 cm but the car is lifted only 5.0 mm. a)
assuming the jack is 100% efficient. how much force must the person exen
on the handle as the car is lifted? (b) if the actual amount of force required on
the handle is 90.0 n, what is the actual efficiency of the jack?

Aballoon is rising vertically upwards at a velocity of 10m/s. when it is at a height of 45m from the ground, a parachute bails out from it. after 3s he opens his parachute and decelerates ata a constant rate 5m/s.when. (a) what was the height of the parachutist above the ground when he opened his parachute? (b)how far is the parachutist from the balloon at t=3s? (c)with what velocity does the parachutist hit the ground? (d)after how long does the parachutist hit the ground after his exist from the balloon?