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GCSE Questions: Forces

Q19. The diagram shows a person using a device called a jetpack. Water is forced downwards from the jetpack and produces an upward force on the person.

(a) State the condition necessary for the person to be able to remain stationary in mid-air.

The forces must be balanced - the resultant force must be zero. This means that the upward force is equal to the downward force (weight).

[1 mark]

(b) The person weighs 700 N and the jetpack weighs 140 N.

(i) Calculate the combined mass of the person and the jetpack, given that the gravitational field strength = 10 N/kg

Combined weight = 700 + 140 = 840 N

weight = mass x gfs

w = mg

m = w/g

m = 840/10 = 84 kg

 

[3 marks]

(ii) Increasing the upward force to 1850 N causes the person to accelerate upwards. Calculate the acceleration of the person and the jetpack.

Force that causes the acceleration = 1850 - 840 = 1010 N

F = ma

a = F/m

a = 1010/84

a = 12.02 m/s2

[4 marks]

[8 Marks TOTAL]