Newtons Laws Revision set 1

In a laboratory, a ball is dropped in a vacuum and falls 200 cm.

Which statement describes the acceleration of the ball?

• It is greater at 10 cm than at 200 cm.

• It is greatest at 200 cm.

• It is smaller at 50 cm than at 100 cm.

• It is the same value at 50 cm as at 150 cm.

Answer explanation

In a vacuum, downward pull of gravity is the only force, so acceleration is constant. Velocity increases at a constant rate. as the ball falls.

A car engine causes a forward force of 100 kN to act on the car. The total resistive force on the car is 20 kN. What is the resultant force on the car?

• 5.0 kN

• 60 kN

• 80 kN

• 120 kN

Answer explanation

+100 kN - 20kN = 80kN

forwards is positive

Four balls with different masses are dropped from the heights shown.

Air resistance may be ignored. Which statement about the balls is correct?

• Ball P has the greatest acceleration.

• Balls Q and R take the same time to fall to the ground.

• The acceleration of ball R is half the acceleration of ball P.

• Ball S has the greatest average speed.

Answer explanation

acceleration of free-fall (objects falling towards Earth) does NOT depend on the mass of the object. S is dropped from greatest height so accelerates to highest speed.

A skydiver jumps from a stationary helicopter and reaches a steady vertical speed. She then opens her parachute.

Which statement about the falling skydiver is correct?

• As her parachute opens, her acceleration is upwards.

• As she falls at a steady speed with her parachute open, her weight is zero.

• When she accelerates, the resultant force on her is zero.

• When she falls at a steady speed, air resistance is zero.

Answer explanation

Se slows down (negative downward acceleration) when she opens the parachute.

Her weight does not change throughout the jump. When she is not accelerating (falling at steady speed), air resistance = weight

A car moves in a circular path as it turns a corner on a horizontal road. The car moves at constant speed.

Which description of the forces acting on the car is correct?

• All the forces are balanced as the car is moving at constant speed.

• The forces are unbalanced and the resultant force acts away from the centre of the circle.

• The forces are unbalanced and the resultant force acts towards the centre of the circle.

• The forces are unbalanced and the resultant force is in the direction of travel of the car.

Answer explanation

Unbalanced forces as the car is changing direction.

The force is at 90^o to motion so it doesn't affect speed and towards the centre of the circle to cause the car to turn in a circular path.

The diagram shows a bird in flight. The bird is flying in a horizontal direction to the right. In which direction does air resistance act on the bird?

• A

• B

• C

• D

Answer explanation

The bird is flying in direction B, so air resistance must be in the opposite direction.

A man can either take an escalator or a lift to travel up between two floors in a hotel.

The escalator takes 20 seconds to carry the man between the two floors.

The useful work done against gravity is W. The useful power developed is P.

The lift takes 30 seconds to carry the same man between the same two floors. How much useful work against gravity is done by the lift, and how much useful power is developed by the lift?

• Useful work done against gravity by lift: more than W

  Useful power developed by lift: less than P

• Useful work done against gravity by lift: more than W

  Useful power developed by lift: P

• Useful work done against gravity by lift: W

  Useful power developed by lift: less than P

• Useful work done against gravity by lift: W

  Useful power developed by lift: P

Answer explanation

Work done is the same as vertical height is the same.

Power is lower as time is longer.

The engine of a motor vehicle develops a large amount of power. Which statement is correct?

• The driving force acting on the vehicle must be large.

• The engine must have a very large volume.

• The engine must transfer large amounts of energy each second.

• The vehicle must be very fast.

Answer explanation

Power is the rate of energy transfer (watts are joules per second).

A man pulls a truck a distance of 20 m, as shown in the three diagrams.

Which statement concerning the work done against gravity is correct?

• Most work is done in 1.

• No work is done in 3.

• The work done in all three is equal.

• The work done in 1 and 2 is equal.

Answer explanation

Highest vertical height gain in picture 1

The picture shows a man pushing a box.
Some of the forces are shown.

Which force is friction?

• A

• B

• C

• D

Answer explanation

Friction is in the opposite direction to the way the box is being pushed.