Newton's first law | Exit Quiz | Oak National Academy

Match the key word to the definition.

• stationary

• a force that pulls objects towards the Earth

• resultant force

• a change in speed or direction of movement

• gravitational

• not moving

• friction

• the sum of the forces on an object accounting for direction

• acceleration

• force between two surfaces in contact when one tries to move

Answer explanation

Friction acts between solid surfaces and gravity pulls things to Earth. The resultant is the sum of forces on an object. Stationary objects are not moving. An object that is accelerating is changing speed or direction.

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Which of these is an example of an object that has no propelling (forwards acting) force?

• A car speeding up as it travels along a road.

• A rocket taking off from a launchpad.

• A shopping trolley being pushed by a customer.

• A marble rolling along a flat desk.

• A sled being dragged by some dogs.

Answer explanation

The marble has no force pushing or pulling it forwards, it is unpropelled.

Which of these are true when there is no resultant force acting on an object?

• It cannot be moving.

• It must be moving.

• If it is stationary it will remain stationary.

• If it is moving it will stay moving at the same speed in the same direction.

• If it is moving it must change speed or direction.

Answer explanation

When there is no resultant force these is no change of speed or direction. This applies even if the object is not moving (stationary).

The figure shows two forces acting on a lorry. What is the resultant force on the lorry?

• 0 N

• 400 N backwards

• 400 N forwards

• 1600 N backwards

• 1600 N forwards

Answer explanation

The forces oppose each other so the resultant is 1000 N (forwards) - 600 N (backwards) = 400 N forwards.

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The figure shows two forces acting on a moving lorry. What will happen to the lorry?

• It will stop moving immediately.

• It will speed up.

• It will slow down.

• It will start moving backwards.

• It will stay at the same speed.

Answer explanation

The resultant is 600 N (backwards) - 500 N (forwards) = 100 N backwards, this means the lorry will gradually slow.

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A bowling ball is launched from a ramp along a bowling alley as shown in the figure. Which of the following statements are true?

• The ball is at its highest speed at point B.

• There is no force acting forwards between B and C

• There is no resultant force on the ball between B and C.

• The ball speeds up between points B and C.

• A frictional force acts on the ball between points B and C.

Answer explanation

The ball speeds up as it moves down the ramp (between A and B) and then slows along the track due to friction, so its at its highest speed at B. It is unpropelled after it leaves the ramp, after point B.

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