Question

In 2014, physicists from FOM Foundation at the University of Amsterdam introduced a new hypothesis of how the Pyramids at Giza were built. The group of physicists suggestedthat ancient Egyptians wetted sand in an effort toreduce friction and then pulled the 3000 kg stoneblocks to their final resting place. 15 men couldmove a block at a rate of 0.5m/sby pulling a largerope angled at 30owith respect to the plane anda tension of 7,200 N.
Required:
a. What is net work done on block?
b. What is speed of blck after it moved .25m?
c. What is work done by block if kinetic friction coefficient is 0.3?
d. What is net work including friction?

Answer 1

Answer:

The correct answer is:

(a) 0

(b) 0.5 m/s

(c) 7740 N

(d) 0

Explanation:

The given values are:

mass,

m = 3000 kg

Tension,

T = 7,200 N

Angle,

= 30°

(a)

Even as the block speed becomes unchanged, the kinetic energy (KE) will adjust as well:

⇒ $\Delta K =0$

By using the theorem of energy, the net work done will be:

⇒  $\Delta K =0$

(b)

According to the question, After 0.25 m the block is moving with the constant speed

= 0.5 m/s.

(c)

The given kinetic friction coefficient is:

u = 0.3

The friction force will be:

= $u(mg-Tsin30^{\circ})$  

On substituting the values, we get,

= $0.3[(3000\times 9.8)-(7200\times 0.5)]$

= $0.3[29400-3600]$

= $0.3\times 25800$

= $7,740 \ N$

(d)

On including the friction,

The net work will be:

⇒ $\Delta K=0$