Physics Answers

A small alien species with many tiny eyes is discovered. After analysis, we learn that light is focused on their transparent retina after being reflected off a concave mirror located at the back of their eyes. Assuming the eyes of this species only consist of a concave mirror with a radius of curvature of 420 µm immersed in a medium with a refractive index of 1.492:

a) Calculate the refractive power of the alien eye. (2 marks)

b) Where should the retina be placed to obtain the sharpest possible image for an object located 1.25 mm in front of the mirror? (3 marks)

A box of mass 5.5kg is resting on a surface and is attached to a hanging 1.0kg bucket by 

lightweight string and a frictionless pulley. The coefficient of static friction between the surface and the box is us=0.40.

a) How many grapes (mgrape =16g) can a student put in the basket without moving the box? T/3

b) When just enough whole grapes have been added to the basket, the system begins to move. If the coefficient of kinetic friction is pk=0.34 between the box and the surface, calculate the

acceleration of the bucket and the tension between the box and bucket. T/4

Objects with masses of 157 kg and 768 kg are separated by 0.342 m. A 28.7 kg mass is placed midway between them. 0.342 m b b 157 kg 28.7 kg 768 kg Find the magnitude of the net gravitational force exerted by the two larger masses on the 28.7 kg mass. The value of the universal gravitational constant is 6.672 × 10−11 N · m2 /kg2 .

If a kettle uses 0.25 kW and you run the kettle every morning for 10 minutes. How much energy are you using in a week?

a force acts on a 2kg mass and gives it an acceleration of 3 m/s^2. What acceleration is produced by the same force when acting on a mass of 4kg?

A 10 kg block of metal measuring 12 cm x 10 cm x 10 cm is suspended

from a scale and immersed in water. The 12 cm dimension is vertical, and

the top of the block is 5 cm below the surface of the water as shown in the

figure.

(a) What are the forces acting on the top and on the bottom of the block?

(b) What is the reading of the spring scale? 86.2 N

(c) Show that the buoyant force equals the difference between the forces

at the top and bottom of the block.

A lorry of mass 10Mg reaches a speed of 63km/h in 20s, starting from rest with uniform acceleration. It travels 2km at this speed and is then brought to rest in a distance of 125m.

Determine: (a) the momentum at 63km/h

(b) the accelerating and braking forces required.

Four identical spheres of masses 2.0 kg each and radius 0.25 m are situated at the four corners of a square. One side of the square measures 3.00 m. Find the moment of inertia about an axis. passing through one of the masses and perpendicular to its plane

What is the formula to get the time interval

a man weighing 160 pounds stands on the floor of an elevator what force will be exerted on the floor what if it descends with a uniform acceleration of 1 ft ft per second square and ascends with a uniform acceleration of 1 ft per second square