Key Homework Dynamics

NAME…………………………BLOCK……

PHYSICS KEY HOMEWORK:

Dynamics Date due:……………….. [Max mark:20 Grade boundaries: A:17; B:15; C:13; D:11; E:9] Note: show the formula you use and the substitution of numbers. Don’t forget units. Use the data supplied on your formula/data sheet 1. The image shows a Harrier Jump Jet hovering above the ground:

(a)(i)The mass of the Harrier is 8150 kg. Determine the weight of the Harrier. [2 marks] Weight = Mass × Gravity 79951.5 = 8150 x 9.81 Weight = 79951.5 N (ii)Determine the upward thrust from its Rolls Royce engines whilst it is hovering, explaining how you have got your answer. [2 marks] Upward Thrust = 79951.5 N The forces are balanced whilst the aircraft is hovering. (b)The thrust from the Harrier’s engines is now increased so that it accelerates upwards at 2.0 m s-2 . (i)Calculate the resultant upward force on the Harrier. [2 marks] Force = mass x acceleration 16300 = 8150*2 Force = 16300N 1

(ii)At this instant the upward thrust of the engines is 98,000 N, calculate the air resistance acting on the Harrier as it accelerates upwards. [2 marks]

2.A man is pushing a shopping trolley of mass 28.0 kg at a steady speed of 1.20 m s-1 in Tesco. Friction acts on the trolley opposing the force exerted by the man, so there is no resultant force on the trolley, so it moves at a steady speed. The man stops suddenly letting go of the trolley, which rolls on for a distance of 1.96m before coming to rest. (a)(i)Calculate the deceleration of the trolley [2 marks]

(ii)This deceleration is caused by the frictional force acting on the trolley. Calculate the average size of this frictional force [2 marks]

(b)The man now catches up with the trolley. He pushes the trolley so that it accelerates from rest up to a speed of 1.20 m s-1 in 0.900 s. (i)Calculate the trolley’s acceleration [2 marks]

(ii)Calculate the resultant force on the trolley during the 0.900 s. [2 marks]

(iii)How much force did the man have to apply to cause the trolley to speed up from rest to 1.20 m s-1 in 0.900 s. [2 marks]

(c)The man continues pushing the trolley at 1.20 m s-1. However he is momentarily distracted and collides into a display of cut price Heinz baked beans exerting a force of approximately 50 N on the display. What force was exerted by the display on the shopping trolley during the collision? Explain your answer. [2 marks] 2

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