Blockchain and its Applications | Week 5

Course Name: Blockchain and its Applications

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These are Blockchain and its Applications Assignment 5 Answers

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Q1. What is the limitation of using the consensus algorithm Proof of Work (POW)?
a. A lot of mining power is wasted as only one gets success in mining at a time
b. PoW is used for permissioned blockchain
c. Low transaction throughput
d. It is used for blockchain mining

Answer: a, c

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Q2. Which statement(s) is/are true for PoS(Proof of Stake) consensus?
a. Depends on the work done by the miner
b. Depends on the amount of crypto currency the miner holds
c. Provides less protection in general
d. None of the above

Answer: b. Depends on the amount of crypto currency the miner holds

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These are Blockchain and its Applications Assignment 5 Answers

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Q3. Which of the following is/are applicable for POET(Proof of Elapsed Time) consensus
a. Each participant in the blockchain network waits a random amount of time
b. The first participant to finish becomes the leader for the new block
c. Trusted execution platform and attestation are used to verify that the proposer has really waited
d. None of the above.

Answer: a, b, c

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Q4. Proof of Burn consensus algorithms do not consider virtual resources or digital coins for participating in the mining activity?
a. True
b. False

Answer: b. False

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These are Blockchain and its Applications Assignment 5 Answers

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Q5. 5 ether equals
a. 5X(10^16) wei
b. 5X(10^8) wei
c. 5X(10^6) wei
d. 5X(10^18) wei

Answer: d. 5X(10^18) wei

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Q6. Which of the following syntax is correct to write data in a smart contract using solidity
a. myContract.methods.store(“99”).set()
b. myContract.methods.store(“99”).send()
c. myContract.methods.write(“99”).send()
d. myContract.methods.write(“99”).set()

Answer: b. myContract.methods.store(“99”).send()

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These are Blockchain and its Applications Assignment 5 Answers

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Q7. How an attacker could manipulate the transaction history of a blockchain to be able to spend a token or a cryptocurrency twice.
a. The attacker hard-forked the network and created a new blockchain network.
b. The attacker modified the transaction on his node and propagated it in the network.
c. The attacker modified the smart contract and recovered the investor’s cryptocurrency.
d. The attacker gained control of more than 51% of the network’s computing power.

Answer: d. The attacker gained control of more than 51% of the network’s computing power.

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Q8. What library/API is used for smart contract deployment and invocation from Dapp?
a. Contract
b. web3
c. admin
d. eth

Answer: b. web3

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These are Blockchain and its Applications Assignment 5 Answers

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Q9. What is the CLI command used to send ethers after the nodes have been initialized?
a. eth.submit Transaction()
b. eth.sendIBANTransaction()
c. eth.sendRawTransaction()
d. eth.sendTransaction()

Answer: d. eth.sendTransaction()

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Q10. In which scenario is a smart contract the best solution to the problem?
a. A restaurant manager wants to force customers to pay for their food by transferring cryptocurrency to his wallet.
b. A chief engineer wants her smart watch to notify her when her partner enters their front door.
c. A grid company wants to automatically buy power when the price reaches a predetermined rate.
d. An insurance company wants to pay out a small vendor whenever the case manager feels it is best to do so.

Answer: c. A grid company wants to automatically buy power when the price reaches a predetermined rate.

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These are Blockchain and its Applications Assignment 5 Answers

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