Sec 3 Physics Dynamics topical questions

Classify each force as contact or non-contact: air resistance, gravity, tension in a string, magnetic attraction.

A student has a 1.5 kg bag of sugar. Take g = 10 N/kg.

1. (a)Calculate its weight.[1]
2. (b)State which instrument measures weight and which measures mass.[2]

A trolley of mass 4.0 kg is pushed with a resultant force of 10 N.

1. (a)Calculate the acceleration.[2]
2. (b)The same force now acts on a 8.0 kg trolley. State and explain what happens to the acceleration.[1]

A 0.20 kg apple hangs from a twig. A breeze pushes it sideways with a horizontal force of 0.60 N until the stem holds it at an angle.

1. (a)Calculate the weight of the apple.[1]
2. (b)Draw the free-body diagram of the apple at rest in the breeze, labelling all three forces.[2]
3. (c)Calculate the tension in the stem.[2]
4. (d)State the angle of the stem from the vertical, using tan.[1]

A car of mass 800 kg tows a caravan of mass 500 kg. The driving force on the car is 2600 N and total resistance on car and caravan is 600 N.

1. (a)Calculate the acceleration of the car and caravan together.[3]
2. (b)Calculate the tension in the tow bar pulling the caravan, if the caravan’s resistance is 250 N.[4]

A ball of mass 0.50 kg is falling. At one instant its speed is 6.0 m/s and the drag on it is 3.0 N. Take g = 10 N/kg.

1. (a)Calculate its weight and the resultant force at this instant.[2]
2. (b)Calculate its acceleration at this instant.[1]
3. (c)State the value of the drag when the ball reaches terminal velocity, and the acceleration then.[2]
4. (d)Explain why the acceleration changed between the two moments.[1]

A student pushes a 6.0 kg box across a floor with 27 N and it accelerates at 2.5 m/s².

1. (a)Calculate the resultant force on the box.[2]
2. (b)Calculate the friction force.[2]
3. (c)The student pushes with the same force on a second, identical box stacked on top. Describe the effect on the acceleration, with a reason.[1]

A parachutist of mass 80 kg falls from an aircraft. Take g = 10 m/s².

1. (a)Calculate her weight and state her initial acceleration.[2]
2. (b)At 30 m/s the drag is 500 N. Calculate her acceleration and describe the shape of the velocity–time graph up to this point.[3]
3. (c)She reaches a terminal velocity. State the drag at that speed.[1]
4. (d)The parachute opens and drag becomes 2000 N. Calculate her new acceleration and state what happens to her speed.[2]

A traffic light of weight 60 N hangs from two cables. Cable A pulls up and to the left at 37° above the horizontal; cable B pulls horizontally to the right. (sin 37° = 0.60, cos 37° = 0.80.)

1. (a)Draw the free-body diagram of the light, showing all three forces.[2]
2. (b)By resolving vertically (or by a scale triangle), calculate the tension in cable A.[3]
3. (c)Calculate the tension in cable B.[2]

A crane’s hook hangs a 500 kg load. The load is lifted upwards and its speed rises steadily from 2.0 m/s to 6.0 m/s in 4.0 s. Take g = 10 N/kg.

1. (a)Calculate the acceleration of the load.[2]
2. (b)Draw the free-body diagram of the load and calculate the tension in the cable.[4]
3. (c)State the tension once the load moves up at a constant 6.0 m/s.[1]

A student claims: "When a car brakes sharply, a force pushes the passengers forward against the seat belt." Assess the claim using Newton’s laws, naming every force and body correctly.

1. (a)State what force actually acts on a passenger during the braking, and which body exerts it.[3]
2. (b)Identify the correct reaction partner of that force.[2]
3. (c)Rewrite the student’s statement correctly.[1]

A box of mass 30 kg sits on a ramp inclined at an angle where sin θ = 0.60 and cos θ = 0.80. The box slides down at constant velocity once released. Take g = 10 N/kg.

1. (a)Calculate the weight of the box and the component of the weight along the ramp.[2]
2. (b)State the friction force while the box slides at constant velocity.[2]
3. (c)Calculate the normal force from the ramp.[2]
4. (d)The ramp is now oiled and friction halves. Describe the new motion, with a calculation.[2]