A child pulls a wagon to the right with 60 N while a friend pulls it to the left with 25 N. What is the net force on the wagon?

Two sled dogs pull a sled forward with 120 N and 80 N while friction from the snow pushes back with 60 N. What is the net force on the sled?

A box rests on a table. Gravity pulls it down with 50 N and the table pushes it up with 50 N. What is the net force on the box?

In a tug of war, the red team pulls the rope to the left with 400 N and the blue team pulls it to the right with 450 N. What is the net force on the rope?

A rocket sitting on the pad fires its engine, which pushes up with 3,000 N. Gravity pulls the rocket down with 2,200 N. What is the net force on the rocket?

Three forces act on a puck along one line: 12 N east, 5 N east, and 20 N west. What is the net force on the puck?

A car's engine pushes it forward with 5,000 N. Air resistance pushes back with 1,200 N and road friction pushes back with 800 N. What is the net force on the car?

A weather balloon is pushed up by the air with 14 N while gravity pulls it down with 9 N. What is the net force on the balloon?

Two ropes pull a sled forward, one with 30 N and one with 45 N, while friction pulls back with 15 N. What is the net force on the sled?

An elevator cable pulls up on a car with 9,000 N while gravity pulls the car down with 9,500 N. What is the net force on the elevator car?

Three students push a cart along one line: 18 N north, 18 N south, and 6 N north. What is the net force on the cart?

While a parachutist falls, gravity pulls down with 700 N and air resistance pushes up with 450 N. What is the net force on the parachutist?

A hot air balloon is rising. The upward push from the hot air becomes exactly equal to the downward pull of gravity. What happens to the balloon's motion after that?

A textbook lies on a desk. The desk pushes up on it with the same size force that gravity pulls down. What is the book's motion?

A hockey puck slides east across the ice. A player's stick gives it a net force of 4 N to the east for one second. What happens to the puck during that second?

A bicycle is rolling forward when the rider squeezes the brakes, giving a net force backward on the bike. What happens to the bicycle's motion?

A spacecraft coasts far from any star with its engines shut off and no measurable forces acting on it. It is traveling at 8 km/s. What happens to its motion?

An elevator is moving upward while the cable pulls up on it with more force than gravity pulls down. What happens to the elevator's motion?

A soccer ball rolls across level grass after a kick. The only horizontal force on it is friction from the grass. What happens to the ball's motion?

If two forces on an object are equal in size and point in the same direction, the forces are balanced.

An unbalanced force is needed to change an object's speed or direction.

A loaded wagon is at rest. Two children push on opposite sides with equal forces of 80 N. What happens to the wagon?

A jet airliner flies level in a straight line at a steady 250 m/s for ten minutes. What does that motion tell you about the forces on the jet?

A ball rolls down a ramp and its speed increases the whole way down. What does that show about the forces on the ball?

A truck moving north slows steadily from 20 m/s to 5 m/s. What is the direction of the net force on the truck?

A parked truck sits on a steep hill and does not move for an hour. What does that tell you about the forces on the truck?

A student claims a moving object must have a forward force pushing it. A puck glides across smooth ice at a steady speed with nothing touching it. Which reasoning uses that evidence best?

A skydiver falls faster and faster, then her speed stops changing and stays steady. What does the steady speed show about the forces on her?

An elevator is moving upward and slows down as it nears its floor. What is the direction of the net force on the elevator?

A team claims an unbalanced force acted on a box during a test. Which measurement supports that claim?

An object sitting still on the ground has no forces acting on it.

Two lab carts roll toward each other and collide. One cart bounces back the way it came. What does the change in that cart's motion show?

A worker pushes a crate across a level floor with 250 N and the crate moves at a constant speed. How large is the friction force on the crate?

A toolbox hangs motionless from a rope. Gravity pulls down on the toolbox with 60 N. How hard does the rope pull up on it?

An airliner flies level at a steady speed. Gravity pulls down on it with 90,000 N. How large is the upward lift force on the airliner?

In a tug of war the rope stays still. One team pulls with 620 N. How hard is the other team pulling?

Two forces act on a block that stays at rest: 40 N east and 15 N west. What third force would keep the block balanced?

An elevator car rises at a constant speed. Gravity pulls down on the car with 7,500 N. How hard does the cable pull up on the car?

A submarine hovers at a constant depth without rising or sinking. Gravity pulls down on it with 40,000 N. How large is the upward buoyant force from the water?

Two forces act on a cart: 12 N north and 20 N south. What single added force would make the forces on the cart balance?