Free Body Diagrams Practice

Which of the following scenarios could be described by this free body diagram?

• A block hangs from a rope.

• You drag a box to the right at a constant speed.

• A notebook sits motionless on a table.

• A weight hangs from a spring.

Answer explanation

In this example, there is a normal force so you know something must be on a floor, table, or other large surface. Also, there is no applied or friction force, like there would be if you were dragging an object.

Tags

NGSS.HS-PS2-1

A car accelerates to the right from rest. Which of these free body diagrams is correct for that scenario?

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Answer explanation

Since the car is accelerating, the applied force must be larger than the frictional force!

Tags

NGSS.HS-PS2-1

A ball is moving across a frictionless surface at a constant speed. Which of these would be the correct free body diagram?

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Answer explanation

Since the ball is moving on a "frictionless" surface, there is no force of friction. However, it is also moving at a constant speed, which means that all the forces must be balanced. Therefore there is also no applied force.

Careful--just because something is moving doesn't mean there's a force in that direction! If something is accelerating then it must have a force in that direction.

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NGSS.HS-PS2-1

A skydiver is falling at a constant speed. Which of the following is a free body diagram of the skydiver?

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Answer explanation

If the skydiver is falling at a constant speed, the two forces must be the same length. Otherwise the skydiver would be accelerating.

In this case, there must be air resistance because otherwise, the skydiver would be accelerating due to gravity since nothing would balance the gravity.

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NGSS.HS-PS2-1

Which of the following scenarios match this free body diagram?

• You push on a table and it doesn't move.

• A notebook rests on a table.

• A block slides to a stop across a surface.

• You push on a box and it moves at a constant speed.

Answer explanation

In this case, there is a net force in the x direction, so the object must be accelerating. It can either be speeding up or slowing down. The only scenario where that is happening is the one where the box is sliding to a stop due to friction.

Tags

NGSS.HS-PS2-1

Which of the following scenarios matches this free body diagram?

• A skydiver falls at a constant speed.

• A notebook sits on a table.

• After a ball is thrown, it flies through the air, accelerating downwards. Ignore air resistance.

• An elevator, which is held up by a rope, accelerates downwards.

Answer explanation

There is only a force of gravity in this example, so the forces are not balanced. That means that the scenario must include acceleration. The elevator example includes a tension force, so that leaves us with the ball after it has been thrown.

Remember, once you let go of a ball, there is no longer an applied force!

Tags

NGSS.HS-PS2-1

A block hangs motionless from a rope. Draw a free body diagram of the block.

Answer explanation

Since it's being held up by a rope, the upward force is tension.

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NGSS.HS-PS2-1

Two people push on a table and it slides across the floor to the right. Draw a free body diagram of the table.

Answer explanation

Now there are two applied forces for the two people pushing on it.

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NGSS.HS-PS2-1

An elevator hanging from a rope accelerates upwards. Draw a free body diagram of the elevator.

Answer explanation

The elevator is accelerating upwards, so the tension force must be longer than the gravity force.

Tags

NGSS.HS-PS2-1

A car turns on its engine and accelerates to the left. Draw a free body diagram of the car.

Answer explanation

Remember, if it is accelerating left then there must be a net force in that direction.

Tags

NGSS.HS-PS2-1