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Questions on Forces

Q4.

(a) A railway engine is being used to try to pull a wagon along a level track. The wagon's brakes are on, and the wagon does not move.

(i) Draw one arrow on the diagram to show the direction of the force which prevents the wagon from moving.

the mark is for an arrow pointing to the left as shown - the arrow may be anywhere on the diagram

1 mark

(ii) Is the force which prevents the wagon from moving greater than, equal to or less than the pull of the engine?

It is equal to the pull of the engine.

1 mark

(b)

(i) When the wagon's brakes are off, the engine pulls the wagon forwards. A frictional force also acts on the wagon. In what direction does the frictional force act?

The frictional force acts backwards -‘in the opposite direction to the movement’

1 mark

(ii) The pull of the engine is 5000 N. When the wagon's speed is increasing, how large is the frictional force?

It is accelerating therefore the forward force 'wins'.

A
 zero
B
 between 0 and 5000 N
C
 5000 N
D
 more than 5000 N

1 mark

(c) After a while, the wagon travels at a steady speed. The engine is still pulling with a force of 5000 N. How large is the frictional force now?

If it is at a steady speed there must be no net force (terminal speed). The forces must be equal in size but opposite in direction.

A
 zero
B
 between 0 and 5000 N
C
 5000 N
D
 more than 5000 N

1 mark

Maximum 5 marks