A75.0 kg man sits on a massless cart that is on a horizontal surface. the cart is initially stationary and it can move without friction or air resistance. the man throws a 5.00 kg stone in the positive direction, applying a force to it so that it has acceleration +3.50 m/s2 as measured by a nearby observer on the ground. what is the man's acceleration during the throw, as seen by the same observer? be careful to use correct signs.